I understand your point. However, there are way more examples of college coaches jumping to the NFL and failing than succeeding.
You can point to Harbaugh....I will point to Davan, Spurrier, etc.
I have no idea if Kelly will make the move or be a success. But cherry picking one example to make a point without acknowledging the many examples that refute that same point is ridiculous.
i think there's probably more coordinators failing at the next level than college HCs failing to make the transition. of course that's because the league tends towards, for lack of a better word at the moment, nepotism or cronyism in that they tend to stick to their own. the league's culture is incredibly resistant to change. they don't hire outside of the NFL generally, not because people aren't qualified, but because they aren't in the NFL 'club'. every once in a while you find coaches that the NFL wants to bring into their club. harbaugh was one. kelly is another one. schiano is one that the league didn't want, btw. they pretty much hated the guy because he was a prick to NFL people while he was a college coach.
the reason that college coaches fail at the next level isn't because of the Xs or Os...it's because of the rest of the job...the lack of control over the team compared to college, managing egos, developing relationships with the players, garnering respect, getting the players to buy in, trying to control too much of what happens...the list goes on.
saban was considered by the dolphins to be too strict and anal.
butch davis just wasn't trusted by the browns players
petrino didn't/couldn't relate to the players
spurrier was viewed as being just too bullheaded and set in his ways
carroll was too buddy-buddy with his players.
these are all things, tho, that coordinators have problem with in addition to having to learn how to manage a whole team instead of just one aspect.
basically, tho, either you've got it or you don't. it doesn't matter where you come from. if you have the right people around you, can learn the rules/regulations and have them second nature, are adaptable and flexible, and can get the players to buy into what you want to do...your vision, basically lead
them and make them want to follow you and believe in you then you can pull it off.