Space Marine 2 settled on 3-player co-op because having 4 lore-accurate 40K marines made it too much of 'a massacre'

pcgamer.com:

Space Marines in Warhammer: 40k are so legendary that even I, as someone who has not painted a single miniature, am aware of how terrifying they're supposed to be. Just to be certain, however, here's a list of facts about these genetically-modified walking tanks that I'm finding out today:

I'm actually having to stop myself, because this isn't even a third of the absurd genetic modifications a Space Marine is outfitted with. This legendary allergy to dying makes them pretty dang hard to represent in a videogame, as per an interview with Yann François, brand and creative manager for Saber Interactive's upcoming Space Marine 2 (the full version of which you can find in PC Gamer magazine's upcoming 400th issue).

«When you are reading about Space Marines,» François says, «Ultramarines and Primaris—you discover that they're superhuman on a really crazy scale. They measure up to [two to three] metres, they have two or three hearts functioning.»

Because of this absurd power scaling, when discussing how many players to allow in the game's co-op mode, François says the team tested out having four of these absolute units on the battlefield. It just didn't work:

"[It] was quite a challenge for the team to say: 'OK, [Space Marines] are almost invincible. How do we create a challenge around it?' Because it could be super easy … That is what led to the choice of creating a multiplayer of up to three players. Because many people asked 'why is it not up to four players?' They tried it, and they realised it was too easy … it was a massacre. So three was a good number."

Aside from being a crowd, a magic number, and what comedy comes in, I can definitely see why they kept it locked to three—naturally, they could just shift some numbers around behind the scenes, but these are Space Marines, dangit. Making them weaker is heresy of the highest order. You could also add more enemies, but this is a game that's already swarming you.

Forcing players to become the three musketeers seems like