I think NFL quarterback might be the hardest job in all of sports. You have to have the tools (I think Newton does), but you also have to study and prepare. Many of the plays a QB makes on Sunday are a result of something they saw while studying film on Wednesday. It is a full-time job. Good defensive coordinators will rip an unprepared quarterback. I am not convinced that Newton will put in the work necessary to be one of the elites. Time will tell.
Edited to add this: Big money changes some of these guys. Some guys lose their drive and get lazy when they get millions. After you give them $20 million, they have other stuff to do besides study a playbook or get to the facility at 6:00 AM to watch film. Look at Peyton Manning, Tom Brady, etc. Those guys aren't playing for the money anymore. They've already got more than they could ever spend. Something is pushing them to win other than big bucks. It is their competiveness, desire to win and achieve, etc.