Brainy's just had so many memorable storylines that it's hard to imagine a Legion book without him. Oh, he doesn't need to be an active Legionnaire, but just knowing he's out there somewhere and can step in whenever things really get out of hand is a major comfort.
And while I used to like Brainy a lot, Ibby, this is the problem. He's out there, and as soon as a bad writer or one that's stuck with no way out of the hole they've written themselves into, we'll get a legionnaire taking off on a mysterious mission, only to turn up at the last second with Deux-Ex-Machina Lad. Thats even worse than revolving death door lad.