What they need is for Alexeyev to become Karl Alzner. So far, apparently, it hasn't happened.
As for Backstrom, his situation is a real puzzle. He is injured; the question is, is it fixable/rehabbable (a word?), or is this a Brooks Laich situation, where he can never be even remotely like he was before? I think he came back this year when he was "playable" but not really right, because, well, this franchise treats every year as a contending year as long as Ovechkin is on the roster. And who else were they going to put out there at 2C, anyway? McMichael wasn't yet ready, and there's nobody else in the organization who could fill the role long-term. Yeah, we can fake it with Eller in the role for a few games, but it doesn't work longer than that.
I think the consensus opinion is right here: The Caps are stuck, salary-cap wise. They've spent up to the cap to try to give themselves the best roster they can GOING INTO THE SEASON, but they have no in-season flexibility and very little during the off-season trading days. The only way to break the logjam is to get rid of big, franchise-weighing salary. That screams Carlson/Backstrom/Oshie, REGARDLESS of what you think of them. You just aren't going to consistently get franchise-altering players when you consistently pick in the 20's.