kick the writer to choose the artist is never a good decision.It all went wrong when Marvel kicked out Claremont for Jim Lee. No one knew more about these characters than Claremont. And Jim Lee left like, 5 months later to do his own thing with Homage/WildStorm/Image anyways.
Lobdell et all were able to keep the wheel turning through the 90's, but the damage had already been done. Claremont's brief Revolution run wasn't his best work, but it certainly wasn't the worst the franchise has seen either.
I am actually a fan of Morrison's run for the most part(his ending did indeed suck, but I also understand that involves his breakdown with Marvel, on the meta-level also), he reinvigorated the franchise in a way that had not been seen since Claremont first came on board in the 70's. That time also saw the return of Claremont in X-Treme, which was actually quite fun.
The post-Morrison/Claremont era to me is the final death kneel. No More Mutants pulled the rug out from under a fertile concept(a burgeoning mutant population that was indeed set to replace humans within a generation) that was barely explored, and the X-Men have been on a constant decline since.
Obviously the movie rights play heavily into all this as well.
Here's hoping Resurrexion will be a course correction, but given the new realities of the Disney-Marvel mass media era, I don't think X-Men will ever reach the heights Claremont left them at in X-Men #3(1991) again.