I agree that he's annoying, but I don't see it as stemming so much from the "stereotype" angle. For the time period it takes place in, his attitudes might not be too far off-base (as we've discussed elsewhere, you could almost say he ought to be even more extreme). It strikes me not so much as stereotyping, but rather a really awkward attempt at authenticity. Looking at actual quotes and documentation of how the various Indian tribes and their people spoke and acted back then, if one were aiming for authenticity, you're obviously not going to end up with a character like Haytham or Ezio.
The biggest problem is that he has no personality outside of that very shakily "authentic" (and I put that in quotes for good reason) frame of mind. Even in the Homestead missions, when he ought to be a bit more personable, he still comes off as unflinchingly serious, despite the odd smile or two.
They really should have said "to hell with historical authenticity" and just added more life, humor, and overall character to him.