Unfortunately you don't make a good case for God Serena.
I was the first person, one year ago pissed off by the sisters performance but let's be honest if GS had faced Erza at any point in this 100YQ he would lose in the same way, I mean she needed a friendship speech and Nakama Red Pants to one shot Enny so in the end it's not like the sisters were eliminated by weak attacks.
Physical strength and durability are not everything in a fight, sometimes hax and the complexity of magic attacks play a lot on PL. This is the reason why Larcade was promoted by Hiro as the 3rd strongest Spriggan because his hax and area attacks are very invasive and can even affect people stronger than him (Irene and Zeref).
So God Serena is a more impressive fighter than Duke and the Sisters but he would loses to their alchemy magic.
What part wasn't a good case? Let me guess more frightening? Ok then Kirin is the strongest BDSK because Selene said he IS ONE OF THE STRONGEST, reading compreehension dude, reading comprehension
It was still BASE Erza, ENCHANTLESS Erza, which means base Laxus would be already enough and neither Jellal would need to use Orion. And people have to see what is reality and what is headcanon speculation. Erza would have defeated GS if had faced him? Ofcourse she would, she is a protagonist, put a Dragon God to be her matchup and this Dragon God is doomed,
but what we analyze here is what happened in the actual manga. Enny was already very damaged and barely standing before the Nakama Speech, and neither of us have anything to confirm that this Nakama boost give Erza a higher boost than an Enchantment would give.
Then why Hiro usually screw hax merchants? Mavis hyped Larcade, Zeref hyped him as an potential weapon against Acnologia and Larcade compared himself with August and Irene. It's pretty clear that he portrayed as one of the top spriggans but you wanna call me that Signarios are stronger than Serena BECAUSE THEY ARE MORE FRIGHTENING THAN HIM? Frightening magically means powerful now? If it is to misinterpret the characters lines then Kirin is the strongest BDSK. Let's also ignore the Jellal and Laxus rivalry portrayal, the Siganrios hype is above canon, so no feat, portrayal or statement can debunk them, their hype is absolute and above everything, then let's just slander Jellal and Gajeel.
Listen personally i think Irene performance was egregious but there is no way to run from the fact that she is second strongest spriggan. Brandish directly compared her to August, Mavis also hyped her, she have with August a similar panel to Jellal and Laxus panel, so no matter how egregious her performance was she is still August level. But Signarios being stronger than Serena via being more frightening it's a joke. You guys were so fooled by the wrong fan translation ''don't hold a candle'' that it's hard now to believe that you guys were just FOOLED. It's easier to fool than convince people that they were fooled.
And their hax is trash, it was Enny herself who said it, it wasn't me who said ''no more cheap tricks'' it was Enny, or are you gonna tell me that Enny could have used her hax to win against Erza but prefered to use Alchemy Armor just to give Erza a chance to win? I don't belive so, because
i don't belive that Enny is stupid, she didn't lost her cool like her younger sister. Erza said that she just need to destroy their world even knowing about that their hax can turn her into a furry, did you really think that Erza said that if this wasn't the way to counter their hax? Then WHY IT WORKED? She countered it with just raw power and speed, she destroyed Luso world more faster than she could rebuild, simply like that, Serena can also spam very destructive attacks and have lightning and flashy dragon slayer magic to give him a better speed advantage
Duke was two shotted by Lightning Only Natsu, and i challenge anyone to prove here that Lightning Only Natsu is stronger than FLDM Natsu, so i say GS>>>ISDM Gajeel>>>Duke. and before anyone talk about the whiteout Duke was shown to be unable to whiteout two differnt kinds of dragon slayer magic, forget Serena, he is not taking Gajeel.