Your chin ups numbers shouldn't have gone down by that much. I can see them going to 7-8 if you haven't done chin ups in a while.
If you want to get better at chins ups I would do more chin ups.
Bench pressing primarily works your chest and triceps. These muscles don't work during the chin up which is primarily biceps and back.
Push ups is primarily chest and triceps as well. But has more isometric work on your back than doing bench press as your lying down on the bench.
Did you gain any weight since you last did 100 push ups?
Koing