In conclusion, to say who has more AoE: Gildartz or Irene?
The answer is subjective as Irene hasn't shown her full power, but neither has Glidartz. By facts, yeah, I guess you're right, Glidartz has hill busting feats whereas Irene hasn't shown any impressive AoE damaging technique (her attacks must necessarily be above mountain level, though, preceding her hype).
I'm not going to lie here... but all this talk about "mountain busting feats, town level feats, city level feats, etc." is starting to get really annoying.
This has been said over and over again, and I've seen some people argue against this faulted logic.
I don't know how many times I've stressed this, but those calculations are completely meaningless to me.
I'd rather use hype and portrayal to measure a character's strength/power than those calculations.
Long story short, there is no way of measuring damage and megatonnes through your computer screen's pixels and a real life photograph of a mountain.
I've analyzed the calculations before:
It is borderline absurd in my opinion to guess the height, width, and dimensions of a drawn panel and calculate the energy and explosiveness of an attack.
Not only is there a lot of guesswork involve, but the "original creators of those calculations" don't even have any concept about the way TNT works and the units they are using.
Their conversions are sloppy in my opinion and they have no credible foundation to the basis of their conversions and calculations.
If you want to measure Gildartz and August's feats through these calculations, then by all means, go ahead.
But I'll let you know right now that none of that will convince me.
You are very well right. The author does not take into account the size of the mountain meter by meter in order for us to gauge the power of the user who destroyed such mountain; but a panel with a drawing, and our interpretation capabilities, allow us to infer whether we're talking of a hill or a mountain. There's a lot of discussion around whether Glidartz actually bust a hill or a mountain, since the fandom is kind of divided, I appreciate calculations that allow us to gauge whether we are talking of a hill or a mountain. I'm no talking about fan-based calculations of megatons, that'd be absurd. After all, whether a mountain or a hill, Glidartz did no more than fragment it, not bust it like a nuke would.
IMO, August's feat was far more impressive than Glidartz's. Not only in terms of AoE it looked an attack of higher caliber, but an ascendent pillar of lava, nuke-like, of the size of a hill/mountain, carries more DC than a punch capable to fragment a hill/mountain.
What happened to all of you guys that argued by "feats only"?
I just don't think it's sound to argue by feats any longer. A thread like this will always involve some degree of portrayal and hype, since we're debating hypothetical battles... Besides, we're debating hypothetical battles of characters who haven't shown their full power yet. So sound guessing will always be required if we want to compare the likes of August to the likes of Glidartz.
As much as it is sound to think August is weeeeell above Glidartz, there'll always be people led by illogical patterns that will claim otherwise. Illogical to me, ofc.
The person with the better feats at the moment is Gildartz, no question about it.
I have to disagree here. What did Alvarez arc GLidartz show? A town busting punch to the floor and being capable of easy-mid diffing a historia. Whereas Glidartz was stabbed by a giant knife, he withstood the blade like nothing, put Brandish to sleep and proceeded to bust a nuke that was seen from dozens/hundreds(?) of km away. Such an attack should've deintegrated them had it not been for U1. Yes, Natsu included, probably; as he only partially negated the attack, and he did so for a very short period of time until U1 was effective.
Even if such nuke did not impress you, which may be well acceptable (after all we're debating opinions here...), I don't think Glidartz has the ability to null diff a spriggan like Brandish, like August would.
The way Invel and Brandish performed was nowhere near to what we all expected from them.
IMO Invel performed as expected, it was Gray who didn't abide by expectations. He was so much boosted, irrationally... Also, Brandish did fine. I mean she can instakill (it's been stated) and she was only toying with Lucy. It was to be expected Dimaria was above Brandish (and even so, that's an assumption, as Brandish didn't have the will to fight her).
All in all, anyone who talks about Glidartz, Irene, August or a plausible vs between them is gonna be using hype and portrayal, because when it comes to feats, they don't have many.
On another note, I disagree with your statement that "Glidartz cannot gauge full power Serena's power accurately". IMO Mashima was suggesting that Glidartz had full knowledge that had God Serena been 100%, he would've seriously posed a threat to him; so his suggestion was a 50/50. Which makes a lot of sense if you ask me.
Dragons flying is probably the only continent level thing... and maybe Acnologia because he needs a continent to attempt to beat him. 
