I don't see what skill he has that is being compromised by playing 3's.
When he drives, he gets all the way into the lane, and frequently under the basket. It's the tall people standing there that are causing the problems, not the 3 he just beat. I don't recall Hayward ever having a stop and pop game, so I don't see how he's going to suddenly get one just because the guy in front of him is shorter. He doesn't get great separation on his shot, anyway, and ironically playing 3's should help him more than 2's in that regard. 2's tend to play crowding defense whereas 3's are more inclined to back off, stop the drive, and use their length on jumpshots.
If Hayward is going to improve, he's going to need to come off screens ready to shoot. He's obviously going to have to go up at the basket. He's going to need to start shooting runners in the lane which he doesn't currently do. His position has little to do with any of this.