After watching AJs rookie performance I wouldn't consider him a sleeper. I think he's a legit starting fantasy WR this season.
We know it will be tough at times for Jason as a rookie to adjust to the NFL and learn this defense but like you, I think he has the potential to be very good. He'll have to play run-stopper, pass-rusher, and drop into coverage from time to time against NFL talent so my guess is that it's not going to be easy for him right away. Hopefully, he settles in and becomes the impact player we need him to be. He needs to be very good to justify the Day 1 move we made to get him.