Pretty sure the best solution for a Grimmer might be to just cut drastically all fodder and leave hero/boss encounters as in Grimmest.
I think my goal now will be to make a non-PC melting form of Grimmer with retention of hero spawns from Grimmest and just way less of everything else.
Of course, this solution renders the concept of an additive Grimmer+Grimmest mod as not possible, but maybe I can make a Grimmest with some level/stat boosted enemies eventually as a last ditch attempt at making this challenging at higher levels.