The AI RB is more conservative, they aren't throwing out stiff arms between the tackles or anything, they run to daylight and do some moves in the open field but tend to cover up the ball if they see the hit coming. It really doesn't effect the human so much because you can do whatever moves you want to do.
The fumble slider is tied to the overall RB ability to some extent. You'll see less broken tackles, but I think Marshawn Lynch led the league in broken tackles in real life with 80 and no one else was even close. So that's 5 per game in real life. You'll see somewhere between 2 and 5 broken tackles per game with decent backs. And because I have the human tackle lower, you will see more gang tackles.