Kelly made his name with the hurry up no huddle spread and Mariotta. Teams have caught up to the hurry up spread over the last couple years as is always the case when someone does something revolutionary. It takes a bit, but that stuff gets figured out.
Remember John Jenkins killing everyone 80-21 at University of Houston when he brought that Mouse Davis run n shoot to major college football? Remember how quickly he flamed out after UM destroyed him?
Kelly can still be an effective college HC, but he won't win NCs running that offense. Look at all the teams running that stuff and how they've struggled the last couple years to win anything of significance.
Houston didn't fall apart because people learned their offense. They fell apart because they got on probation, and then ended up in C-USA after the SWC collapsed.
Anyway Kelly is a great college coach. Plenty of great college coaches don't make it in the NFL. Just look at Nick Saban, Steve Spurrier, Barry Switzer, Dennis Erickson, Bobby Petrino, Lou Holtz, John McKay, Butch Davids.
Jimmy Johnson is the exception when it comes to CFB coaches moving to the NFL.