He was basically Native American Altair, only he's also native american forest gump in that almost every major historical event in the US at the time of the game runs through him somehow.I'm trying to think of how else he could be written without making people cry foul for turning him white.
He's inherently not going to be able to speak with the same kind of wit that Ezio and Edward do, because the game is about him interacting with a people, culture, and language he's not familiar with. These people have also destroyed his homeland, and even if they hadn't, even if he was somehow on good terms with white people, they'd be predisposed toward treating him differently anyway. He's not going to feel like being wry and witty.
What can you do with a Native American in that time period to make him likable and identifiable? Maybe I'm just not creative enough.
This is about all I can think of, but the movie's mostly a comedy and doesn't pretend to be historic: https://www.youtube.com/watch?v=e_nYT8WhFjk
the biggest issue Connor has is that he had to compete with a better character in Haytham. Connor's ethnicity has little to do with how we perceive him, it's his lack of a personality and the fact that he's almost always more boring than anyone he interacts with.
With Ezio, you initially had a very well developed revenge plot that drove that character. they tried to do the same with Connor, only they probably felt that they couldnt really develop his familial ties without making the beginning of the game 10 hours long. Connor is probably more of a victim of the odd pacing of Asscreed 3 than anything else, really.