Well so far I am not finding core to be that difficult apart from the few encounters. I could feel the difference in the early levels between normal and core in that crits from archers wrecked me, but now on higher levels I just steamroll most mobs without any tactics, I use Nenio for the skill check mostly, unless I need her for some fights. I sometimes want to add Wenduag as the third archer just to see if my front line would manage to get a hit in.
I would really like for Owlcat to do something like a Heart of Fury mode, where they actually add something to the gameplay and not only inflate the numbers.