BookBarbarian
Expert Long Rester
Overkill is pretty much never part of the theoretical discussions because it's too complex to figure out.
Just like there'a always the assumption that GWM will get buffs or advantage that somehow are never applied to the other fighting styles. Or that maybe, just maybe, chasing after DPR doesn't really matter all that much to some people.
For what it's worth, with GWM I'm usually not concerned with overkill as I'm to busy being happy that my bonus action attack got triggered.