As fans will recall, Game of Thrones made them even larger for Season 7, so going even bigger is hard to wrap one’s head around.
Wyverns are actually smaller than dragons, according to Ally Pennell, so Drogon and the rest would possibly have grown beyond their already gargantuan size.
They are still just as powerful as can be, though the legend of Danerys having dragons would require a bit of rebranding.
If Daenerys were riding actual dragons, she might be even more dangerous to her enemies.