One of the main issues I have with Gruden is his lack of patience with young quarterbacks. He wants to come in with his complex offensive schemes and 15-word plays that only confuse younger players. More complicated =/= more productive. He likes Peyton Manning because it takes a QB with that level of experience and football IQ to understand what Gruden is talking about half the time.
Furthermore, he's the type of coach who's own ego is subject to get in the way of team chemistry. His message and his quirks will wear thin on a football team, it's only a matter of time. I don't think he has staying power. Gruden is a flashy name that just seems to like being a flashy name more than anything else.
Cowher and/or Jeff Fisher are both more even keeled, and have more staying power no matter what situation they get into. Their message and quirks aren't going to wear thin on a football team nearly as fast as Gruden.
The spread concepts that the NFL has integrated from college haven't made offenses more complicated, they've made them simpler and less complicated. Which is why college QB's who would've been busting out in the NFL 15 years ago are now able to experience various degrees of success in the NFL.
However, over the long haul defenses are going to force each and every one of these quarterbacks out from under that umbrella of simple spread concepts, and into what the NFL is all about... identifying matchups and exploiting them. The QB's that can't adjust and do this will be cast by the wayside and replaced. The cream will always rise to the top in time, and the sh*t will roll downhill.
As long as Gruden understands that, he'll make a good quarterback out of a good quarterback prospect. But they're going to eventually have to learn Gruden's WCO and philosophy, the spread concepts he implements into it will only keep a young QB hid for so long.... and Gruden's patience will be tested.