I'd have to disagree with you on that, the IA both in game(tabletop) and lit. are able to take down things that the Space Marines can't, yes, the SM are amazing,7 feet tall, blah,blah,blah, but they kind've stand out in alot of places, don't you think? They're good for retaking parts of a planet or a whole system, but when there's really just one thing in the way of the Imperium the IA get called is what I'm saying, and since they all have their own "traditions" for lack of a better word, the gameplay wouldn't always be going toe-to-toe with every,single target, where the Vindicators are good at holding patrols,taking out single figures and that sort of thing from long range, there's the sneakier Eviscerators that engage and kill everything, then there's the shapeshifters, the C-somthing's? that have to keep their real identity a secret waiting for the right moment, and I can see alot of potential there.And I doubt it would be knife to gunfight scenario for most of the things there, if you compare the IA points and scores to other named characters in the game, there's a lot of named space marines that have lower scores in everything, so it wouldn't always be everything but SM and bugs get killed.