Whereas Tom Hulce's version is someone you can empathize with and care for, which I think is important for the story to work -

Oh, yes, for sure. Hulce is amazing in this movie, which I didn't really understand until seeing the play version either. He's both obnoxious sometimes -- you can see why he gets on Salieri's every last nerve -- and at the same time he's got this very sweet innocence about him. And in addition it's clear that he cares very much about music and works hard at it!