Think of it like this, imagine feral druids, now make their head longer, would you want a dragon to be that sized? no, of course not, it would need to be mount sized AT LEAST, and then boom you have a problem, you are now bigger then all of your melee, now movements, swings of your massive wings and tail, it makes it impossible to see, any ability where you lift off would block the entire raid.
there is a reason most size increasing toys break on combat.
it is far easeir to make something bipedal feel large then something quadrupedal.