In an RP sense, I always looked at it as there being a LOT different between the felar and arial races despite sharing hydrophobia.

Arial have a long history of being mages (or having mages among their race). They're relatively smart.

Conversely, felar have more of a history of distrusting magic and being half-assed mages (e.g., anti-paladin, spell-using ranger) at best. They're also a lot closer to their instincts / animal side as a race (see: feral growl, pack sense).

Given these things, arials turning into an animal very antithetical to its nature "feels" more right to me than a felar doing so.