The shape of the story feels like Anakin was aged down late in development and he was meant to cut a more harrowing figure as both a run down victim of generational slavery as well as a target of racism/speciesism all too eager to prove himself

I've never thought of it this way, but that does in fact make the most sense. Lucas swerved at the last minute to make Episode 1 a kiddy movie? I can't imagine he would have needed to do that to secure funding for the then long-awaited continuation of Star Wars, but stranger things have happened.

wasn’t there a thing where the other kids were being demeaning to him about humans being too slow in the head to be good pod racers

Yes, this is a pretty critical plot point, Anakin can only participate as a human because he can use the Force.