It would make a lot of sense to ease Rosen into the job, rather than just throw him in there. We'll see how training camp goes. remembering back to Tanehill's first camp, the plan had obviously been to follow a similar path with Gerard starting and the Ryan taking over, but Gerard got injured and Tanny had to start.
I think Rosen will out perform Fitzmagic in camp but the sensible thing would be to hold him back, we'll see, training camp is going to be fun.
Flores and staff have a LOT of tape on Rosen and I'm certain there are things they want to tweak. A lot of who starts depends on what the staff wants to change, how quickly Rosen picks it up, and what they feel they have in the OL. In any case, IF Rosen starts, he'll have to be unquestionably better than RF. Anything less than that and I suspect they defer to the vet.