Eh, I think the act of DM is itself game design, even if you don't realize, but I guess it's philosophical at this point.
Yeah that's usually why you give multiple option per monster to cover multiple roles that still feel like that specific monster, that match it's style in its own unique way. The Orc Archer shouldn't be just the sames stat as the Orc Ravager with his weapon switched, that's just boring. They should have unique special abilities while still having those unique traits Orcs usually have. The goal is actually to help B make entertaining encounters on their own by giving them a variety of tools they can mix and match.
Maybe you would prefer if we limited that to humanoid monsters?
I can see why that would be interesting. I'd personally use this opportunity to pre-build a couple different liches, and then maybe a Lich template so you can turn any other monster into one so you can use the base role.
That's... that's what we want???? and then you give that goblin a special ability to facilitate that sort of actions.