Why the jump?

Recently I made a post about getting my favourite angry chicken Fae to +5 (highest merge across my account) and taking her into arena with B!Lucina+2, Dorcas, and Arvis pairs me against defense teams with scores of 700-704 and at least 2 5*+10 units and the other at +5 or higher.
Before this when she was only +3 I would see the occasional defense team with 700+ score and have no units really above +5 merge. Has anyone else come across this when going into arena?
I apologize if I come across as whining, I'm just baffled as to why there is a disparaging difference in team comps with the only difference being adding 2 merges to Fae.