Tbh I don’t use either of them much… Grimm is too squishy without emblems (and he’s not getting them off BK and GKong) and Gormek is made completely redundant by Wilbur (who sits at +19 permanently because of BK synergy).
If I wanted one or the other it’s a question of whether I want them to survive (Gormek) or I want the tile damage (Grimm)… But mostly it’s a colour question and you take whichever one the situation calls for.
If you pull at Atlantis, don’t do Gormek as Wilbur is better… If you’re F2P, then go ahead, you’ll find plenty of uses for him.
Also on the 3*/4* thing… Yes you want depth, but hero’s that bring more out of your others are also valuable.
Depending on options and pulling tendencies, I’d probably go ahead with Gormek (red feeders only) at the same time as Bjorn and Nordri.