In all fairness to Long, he may not be the best pass rusher on the team anymore, but he is also a more complete player still. Maybe Quinn passes him up on that but while Quinn has to beat the best O-lineman on the field generally, he is often only single teamed. Long often has to go against two linemen and he is seen by the QB as he approaches. I'm not saying Quinn couldn't get many of those same sacks but let a QB sidestep him and I think he is out of the play a fair amount where as Long seems to stay in it. I think the Rams are smart in not moving Quinn to LDE. He has far more freedom out there on the right and I think you'll continue to see him use that freedom against the run more as well. But Quinn is a sack machine and that is exactly how he should be played.
A side note. Brockers has as many sacks as Suh and has only one fewer tackles. So while Suh will no doubt go to the Probowl, Brockers - I believe - will have a better year and grow to be much more of a monster in the middle. This team has to be a factor in the playoffs - much more that other teams because of years of futility - before Quinn, Long, and Brockers get their just due.