If it was OBVIOUS to them they couldn't move the ball against the steelers because Faine isn't big/strong enough to move the NG, then you make the change. And Faine wasn't THAT high of a pick, he wasn't making as much money as you imply. Plus, I'm pretty sure next season would be the last of his contract anyway, so they aren't losing much money if they trade/cut him.
Not to mention the fact that Bentley is a) a better fit for them and b) flat out one of the better centers in the league and c) WANTED to play for the Browns (his favorite team growing up).
I'm not saying Faine has been good or great. The world isn't black and white to me. I'm just saying he hasn't be a "Major flop".
And, yes, teams do things (to their roster) in order to compete against the better teams in their division. You think we signed Henry cuz he's one of the top CBs in the league, or cuz he matched up well vs TO and Plaxico Burress? Probably a bit of both, but moreso cuz of his ability to matchup against the bigger WRs. Faine didn't match up well vs a powerful NG like Hampton. He doesn't have the room to grow physically enough to be able to handle a powerful NG one on one. So what do you do? Keep him on the team KNOWING he won't get the job done vs the best team in your division, or do you make a change?