But bowser has always been that size in comparison to Mario. NES he was a tiny bit taller, Super Mario 64 he was bigger still, but he's always been displayed as larger than mario, but small enough to be whipped around by his tail. In the Galaxy games, the same deal. He's classically been about that size in comparison to Mario.
Obviously he's obsessed with trying his best to be gigantic so he can stomp Mario (Probably why is FS is Giga Bowser) and a couple game display this (Paper Mario, Mario & Luigi Dream Team, etc) where he gains his unbelievable size with his master work of being an evil dunce that has no fallback on his plans. But regardless, he's definitely applicable for being put in the game without being so absolutely taboo looking. Everyone knows he's a bit bigger than Mario, but Mario still kicks his ass with his bare hands.
Whether Ridley is a dinosaur or a dragon makes no difference on how badly he would look in game. Either be a massive awkward mess of polygons and hitboxes across half the stage or be shrunken to a reasonable size and then look completely stupid.