I understand what you're saying, but since like you said they know themselves better than anyone, how would you explain their meeting? Irene didn't exactly fall in line, and August went as far as to finish the job for her since she stated plainly that she wasn't moving until it was done. Then she said she would only go to "let him save face". As arrogant as you say she is she's never shown to be careless with her words. She wouldn't say something like that unless she could back it up.
You seems to have missed the point though. The Irene we knew has clearly lost her sanity and is emotionally unstable.
She was determined to enchant herself into Erza's body shortly after she was born, but failed because such a feat is impossible. Or apparently so. It turns out Irene was not actually incapable of doing so, but rather she could not bear to go through with it.
She then chose to leave Erza with an orphanage at Rosemary Village for fear of continue being a direct threat to her child due to her own madness. The torture she suffered at the hands of her own people, did not only robbed Irene of her compassion and empathy, but also her sanity.
Irene has a tendency of taking things personally. She turned Hisui into a mouse, and sadistically urged her father to say he loved her despite her transmutation. She was confident he could not bring himself to do so, because her own husband did not maintain much love for her when she started transforming. But was forced to eat humble pie.
Irene was uninformed and did not show any understanding dragonification can be halted. After witnessing Wendy possessing the capability and talent to nullify Irene's high level enchantment with her own, Irene still chose to go ahead and took over Wendy's body, which not only diminishes her magic power, but allows Wendy to enter her original body and used Irene's far superior magic power against her.
Foresighted detected: None.
Irene has a tendency to let her emotions get the better of her, and cloud her judgement. Her decision-making is erroneous, and more often than not make the wrong calls. All these lead to her claims hardly being substantial.
On the contrary, August is calm and collected. His awareness and foresight is noteworthy. He knew FT will identify the Spriggans' location with magic radar, and hid both Jacob's and his positions from it.
August told Brandish sympathisizing with FT would be a mistake. And seconds later, Mest proves him right. He correctly assessed Brandish attacking him was not voluntary, and consequently putting her to sleep rather than hurting her with the rest in return.
August also rightfully deduced the one magic as love, and that could transcend the concept of good and evil, life and death.
He predicted both his, and his parents' fate.
Perhaps, best example to compare August and Irene's mentality was the time they engaged each other in the consequence of casting Universe One. August questioned the effect of the action point, while Irene rebutted it as bringing Alvarez closer to their goals. We all know how it turned out as the spell actually changed the tide of the battle in Ishgar and FT's favour.
And on the topic of their interaction, despite insisting on torturing Mira to her death, August still got dibs on her prey, which clearly surprised and irritated Irene, she changed her tune and acquiesced to August's will . .
Anyone with any fundamental awareness on social dynamics should know who came out of the exchange looking more dominant and of higher status.
August beat Cobra with his precognition ability. He beat Racer by outspeeding and assaulting him. He reflected Midnight's Spiral Pain to defeat Cobra, Racer and Midnight himself.
Though we did not see any panels of Jellal attacking August since he was constantly on the defensive, we do not know how he went down. But according to Jellal's thoughts, he exhausted all options and there was nothing left he could employ from his arsenal. We know of Mashima's soft spot for Jellal, and probably preferred not to humiliate the guy in front of the readers further. It is not unfair to surmise August handled everything we know Jellal has to offer.
He did used Meteor later, so we at least know August is faster than Jellal with Meteor. So August dealt with the continuous assault from Jellal, Midnight, Cobra and Racer, then beat them all at their own game with zero blemishes on him.
As if the defeat was not enough, he left them all alive just because he know none of them can pose a threat or muster a challenge against his side. The next time Jellal showed up, was only after Zeref's defeat when he saved Erza from Acnologia. Let that sink in for a moment. That is how scarily accurate August is.
The one who lived up to his hype. The one who has a - I don't like to use word perfect, but damn son - flawless record against all caster magic. Despite his outrageous strength, August is a combat pragmatist first and foremost.
Usually in storytelling, most authors will choose to give power in compatibility to character flaws. So they could have an achilles heel the protagonists could possibly capitalize on. When the most broken superpower is wielded by the wisest, most competent and sensible character, it becomes terrifying.
Both August and Irene engineered their own death. But Irene's threshold of durability can at least, be quantifiable. She was killed by a sword, enchanted with Wendy's dragon slayer magic, Irene's weakness. The effective quotient is therefore, Erza's sword + Wendy's damage multiplier supercedes Irene's mortality.
Unlike dragon slayer magic on dragons, August is not particularly weak to holder type magic. He can be hurt by it, but the point was rammed home when at the end of their battle, Gildarts' most offensively powerful move move till date allowed him to bypass August's nigh invincibility over caster magic, and land a clean hit. This barely even wounded August.
August was killed because the condition of Ars Magia required him to sacrifice his body as a medium. And we cannot even quantify this property. Mashima did not let August display a move on the same offensive scale as Ars Magia - only without the sacrificial condition - which is what is frustrating.
Otherwise, we all know this discussion would already have been done and dusted with. Defensively, August record remains untouchable. More so than Irene's offence. And most success stories are built on great defence.
When it comes down to it, aside from Acnologia, this level of proficiency has never been seen before or after. No hyperbole, that is what separates August from the rest of these wannabes.
Like you mention there are a lot of assumptions in this tournament and that really doesn't interest me. It's fun to counter assumptions with even bigger assumptions but in the end I've never seen August use DS Magic so I'm not going to assume some vague lines about God Serena being "with him" is proof that he has his abilities now. Just like I'm not going to assume that Irene can use anything stronger than Deus Sema because she's a master enchanter. I go by what I see. Does August defeat Irene in her human form? Of course. Does he defeat her as a dragon? Not in my opinion.
It's such a shame despite the vast repertoire of spells in her arsenal, the chief argument for Irene over August has revolved solely around and heavily banked on her dragon form. Because in her human form, Irene's performance greatly pales in comparison to August. But seeing the stance adopted by Irene's supporters is to relegate her potential to being a flat track bully, let's address this issue.
The conventional belief held by some is that dragons being a higher plane of existence in the magic world, cannot be hurt by regular mage with regular magic. Irene's true form has always been the dragon she has already transformed into. Her human appearance, is, but a facade. Internally, the properties of her core being has never changed.
Irene always had the power of dragon within her. She did not, and could not, utilize it because she was in her human form. Nonetheless, she was bleeding from wounds she sustained. Wounds which were not just superficial, but bleeding from the internal.
Remember it was stated during the elipse gate arc how dragon slayer magic is supposed to harm them? In theory, it should have damaged them. But in practice, unless it is wielded by someone who is powerful enough, it is as useless any other kind of magic. This should also mean power level is related in accordance to damage.
A heavily wounded Erza, aided by an equally wounded Wendy, critically wounded Irene. At the point of exchange, fully transformed Dragon Irene could not resist the damage output from the attack.
When a magic is unbelievably powerful, it can affect dragons too. So much so that, it can be used to make up for the gap in power. When Ultear casted Last Aegis in the eclipse gate arc, it turned back time and reversed everything that took place, dragons included. Future Rogue created dragon supermacy magic and dragons were forced into doing his bidding.
But here comes the interesting part. Not all dragons were affected. Atlas Flame was able to break away from Future Rogue. And in his fight with Motherglare, the latter dragon says his adamantine armour is impervious to even the attacks from other dragons. All this points to conventional power level applying to dragons too.
And talking about Atlas Flame. His flame and spirit was frozen by Silver after he was dead, which naturally means he was at a state weaker than he was before he passed on. So Silver with his magical ability and power enabled him to make up for the difference and effectiveness over a dragon, despite him having no dragon slayer magic.
Which leads us to why August can hurt and harm Irene, regardless whether she is in her dragon form or not. I averted to bring this up, as it is one of the biggest asspulls in the series. But since most of Irene's supporters are unabashed on selling August short, and I only wish to bring up on panel feats, it seems like we don't really have a choice here.
Deus sema casted by dragon Irene was successfully destroyed by Erza. With a single, solitary arm. Now let's sit back and digest this nauseating feat. And it's over. Then we go back to August. The extraordinary being who wields an otherworldly ability with phenomenal consistency. We all know how this would end up.
. I don't think MP affects stuff unless it's cast as a spell. Even Acnologia's MP didn't really trigger anything.
, but I'll still chose Irene my Queen all the way 
. It was a huge area though...
