I think Brown truly believes that the rules for everyone else in the league simply don't apply to him.
He's absolutely bought in to the hype that he's the greatest receiver ever to play the game and that he ought to be allowed particular concessions because of his talent and his output. Sure, he works out like a machine, but that won't matter one bit if he doesn't have timing and rapport with his QB.
Roethlisberger and Brown spent pretty much a decade learning what each other was going to do in just about any game situation. Carr has no idea that Brown will break off a route at any given moment if he sees something in the defender. And if Carr throws the ball to where he THINKS Brown is going, Carr is going to look like a **** QB because as often as not, Brown won't be there.
Sure, he makes some amazing plays, but that's because the plays were there for him to make. Carr isn't going to have the comfort and trust in Brown to just heave **** up and see what happens. I mean, you can know in your head that Brown is amazing and is likely to make a play, but a QB has to trust in his gut that if he makes a risky throw the receiver is going to ball out for him. Can ANYBODY on the Raiders right now believe Brown is going to ball out? He seems much more intent on bailing out.
The time he skipped in training camp WILL have repercussions. Brown is good enough that he'll still put up over 1000 yards essentially in his sleep, but I would be really surprised if he doesn't see a very real dropoff in his production for any number of reasons.
He'll be doubled every single down and Carr may feel more comfortable in those situations throwing to the single covered guy that he's worked with for years or at least through the pre-season.
Brown will change routes and do things that Carr can't anticipate and as a result, Carr may be late in his throws or he may throw to where he THINKS Brown is going to be and that will lead to incompletions and ints. That will, over time, erode Carr's faith in Brown even more.
No, there will be repercussions. It will be interesting to see how well the Raiders can mitigate them and if Browns raw, sheer talent can overcome.