If we were good enough to get to the CFP in 2015 or any year, there would have been the plethora of posters who would have been satisfied with nothing less than a Natty, Alabama or not. The 13-0 that we accomplished to get there would have been out the window and it would have been the same complaints about Kirk, etc. And I will double down that the complaints at that level would have been more venomous than ever. Once again, people were calling for the termination of BO RYAN after he lost a NATIONAL CHAMPIONSHIP GAME.
There's reason to believe we did get as far as we could in 2015. MSU exposed our weaknesses on that final drive, picked on Mabin, forced Lomax to read keys in the open field, and wore us down physically.
Many fans, while disappointed, would have had level heads after such a game, like you said. But many more would have been hanging on to the proverbial ledge by their fingernails.