Bevell has a history of poor pre-game planning, at least that's the best explanation for why our offense sucks in the first half. So much so that there was an ongoing debate about whether Bevell was "setting up" plays in the 2nd half of games, and talk that our team is just all about finishing, so...it's okay they suck in the beginning (it certainly is, until it isn't). I guess Belichick and McDaniels aren't smart enough to plan that far ahead, because the Patriots just came right out and drove down our throat immediately, before the Lane injury even. Bet they feel stupid for trying to succeed on offense right away.
He also has a history of going away from the run at the worst possible moments, for example when the defense is gassed from being on the field, or...what was that other one...oh yeah that time we lost the Superbowl on a quick slant. This talk of "learning" misses the point entirely, Bevell's nature is to get too cute. He values randomness and understands getting good matchups from a formation standpoint, but from a personnel standpoint he fails miserably. Bubble screens that look wonderful in terms of numbers but look sucky when you realize they call for an undersized receiver to block a LB or some other large person one-on-one.
His formations and route concepts aren't complex enough to get his average WRs open, and yes I'm parroting what I've heard from others here and analysts because I can't evaluate that myself, but I haven't actually seen this point be contested much. What I can evaluate myself are the 3-wideouts-in-a-phone-booth plays in the red zone or the fades to Doug Baldwin (although what I wouldn't have given for a fade to Doug last Sunday on the final play instead of what we got). Elementary would be giving those too much credit.
Speaking of red zone, when we aren't running the ball down there, quite often the total blanketing of our receivers (see previous paragraph) results in Russell escaping and connecting with a wideout who has also gone sandlot.
So we have an OC with an embarrassment of riches at RB and a QB that covers up for all manner of mistakes. As well as the laundry list above.
He's not the worst in the world, he's average on a great team. But when I tack on that final play and the fact that this isn't a one-time deal, as soon as he reaches a few months in between Cable beatings he starts getting cute again, I'm ready for him to be gone.
For those worried nobody would want to replace him, there may be some egos that wouldn't, but it's a championship team. Bevell has been average for 3 years and he got HC looks. Someone looking for some career rehab or someone with their eyes on HC someday will I'm sure be able to talk themselves into a job with Seattle. Far, far more easily than they would a crappy or average team.