the fact that Rex got as many HC jobs as he did goes to show that having a big mouth will take you farther than your talent justifies. I don't think Rex is intellectually sophisticated enough to coach in this era. The great coaches make adjustments and adapt to the talent they have. Rex put Mario Williams out in pass coverage.
There are many superior coaching minds who can't get a HC job again (Shanahan, Wade Phillips, Lovie Smith, Mike Smith, Chip Kelly). Ryan doesn't deserve another shot.