Weird Difficulty Jump from 20F to 21F

I just beat Jackson last night (on my first attempt) with a 3-star LV74 Striker, and moved up into 21F and 22F. It seems like LV38 Screamers on 21F are a lot nastier than LV73 Screamers on 20F. Is it just because of their equipment?

EDIT: Thanks for the advice, senpais. Some of it is stuff I suspected, but I appreciate the confirmation.