If we rate RBs by average yards per attempt there isn't a single RB in the top 35. The best running back is a punter named Reggie Hodges.
Why in the world do you think I included the "for backs with lots of carries" provision?
So what did you mean when you said the list of top RBs (by attempts) looked "rather mediocre"? With two exceptions (Benson and Gore, who were just on mindless pound-the-ball losers), it looked like a pretty good representation of the best RBs in the league to me.
I disagree

Less than half of the top ten in attempts / game would make my top ten overall running backs of last season. That Charles kid on the Chiefs played some REALLY fine ball. I don't know if you saw any Chiefs games, but he was running like mad and catching balls whenever he got the chance. For some insane reason, the Chiefs had him split carries evenly with Thomas Jones. Charles had 6.4 yards per attempt, Jones 3.7 yards per attempt. Yet Charles got the ball more. Was he a better back? Hardly.
I saw a lot of Steelers games last season and Rashard Mendelhall was bad. Yeah, he wasn't helped by the blocking, but the total performance was even worse than his very mediocre 3.9 yards per attempt suggest. Yet, the Steelers kept feeding him the ball the tune of 20+ carries a game. Should he be considered one of the top backs last season because of that? Hardly.
Bottom line is, it's quite common for teams to use some sort of running back by committee these days, even for a very good back. There is, IMHO, little correlation between the most heavily used backs in the league and the best backs.
Getting back to Ingram... I just don't think he'll necessarily need to withstand 20+ carries a game. As the stats show, that's fairly rare.