Throughout the series the only animagi we see are Gryffindor's McGonagall, James Sirius, Worm tail, etc the series makes it seem like only Gryffindor's can be an Animagus it has nothing to do with their animal forms it just that we only see a Gryffindor be an Animagus.
We should've seen at least one Animagus that wasn't a Gryffindor, this witch or wizard would've been a Hufflepuff, or a raven claw the animal form could've been a panther, an elephant a hippo or a bull. any animal that can survive in the wild or fight other animals, having an Animagus outside of Gryffindor would've provided some diversity at Hogwarts.
