Hmm... I gotta agree with alexi here. Gigantomachia seems way stronger than that first Nomu, given that he can easily level mountains from what we've seen of him, and he's a smart fighter too.
I was thinking of current Gigantomachia vs. prime All Might or season 1 All Might, but thanks for pointing that out. Gigantomachia was much smaller back then, so my assumption is that he grows stronger over time, which Spinner may have confirmed when he said that Gigantomachia grows larger over time.
As for Mina, they're definitely gonna bring that up in the future. Her and Kirishima will likely face Gigantomachia one day in some way.
Bingo. Assuming you're referring to matchups against the Nomu.
Although, the anime showed Endeavor's ability to burn hot enough to the point of carbonization to prevent cellular regeneration, which is perfect for fighting a regenerating Nomu, but given the events at Fukuoka, I have a feeling that will remain anime-only... Dabi, though, he can definitely do that.
Fair point about the trouble All Might had against the Nomu being due to his quirk... So maybe season 1 All Might would be able to defeat Gigantomachia.