I think you're looking at this a bit backwards. The Jets are built for the run. Having Holmes helps the run as much as the run helps Holmes. You say that the Jets will throw the ball more since teams will be keying on the run, and I agree. However they will still be a run-first offense, and even if Holmes gets off to a great start, teams will start to double him on passing downs. They're going to pass more but I just don't see Holmes having as huge a year as you think he's going to. Holmes is going into an offense that throws the ball less. No matter how you look at it, the Steelers threw the ball more often last year than the Jets will. Not to mention they had a far superior quarterback. Big Ben threw the ball 506 times last year. The Jets will not throw the ball that often, unless they're consistently coming from behind.
I think he'll help the offense, but you are vastly overstating the impact he will have on the offense. 8 catches per game over a 16 game season extrapolates to 128 catches, which would be #2 all time for a single season.