My memory of Derrek Carr is that he struggles on deep balls but it pretty good at the short- to mid-range passes that Brown is so deadly on. I don't really see why he'd struggle to get his catches in Oakland. Maybe not 100, but he'll get tons. They'll likely pass it more than they have in the past now that they have Brown. They were about 8 pass attempts per game fewer than the Steelers last year. Brown was getting nearly 1/4 of the Steelers targets, gotta think he'll get at least that if not more in Oakland. So if the Raiders increase by 2 throws a game and target Brown a little more often than the Steelers did, he will be getting more targets overall.
I think the team will stink, but Brown should still be able to put up huge numbers unless he gets very old, very fast, which I doubt.