Actually a squad of Imperial Guardsmen can take out a small squad of Space Marines fairly easily. The Space Marines (btw I do know what I'm talking about here as I collect both the tabletop game AND play Dawn of War) are not invincible, rather they are pretty much the Warhammer version of the Spartan-II's from Halo or any equivalent character from any equivalent game. However, the Space Marines can put up a decent fight. This would actually be good for an MMO game, whether FPS or RPG, as it promotes teamplay among less well supported troops. Plus, to fit with the ideas of the various races from Warhammer 40K, the races would effectively fit a rock/paper/scissors schematic, but with more options. Any Warhammer player (game or tabletop) will understand that as a basic example, Tau are useful against Orks, who are good against Eldar, who with stealth are very good against Space Marines, who can easily beat Tau. Each race has weaknesses as well as strengths and the Space Marines, being slow and cumbersome (especially Terminators), are no exception.