Benning 14 games last year and has two years on his contract. Put him on waivers and he likely makes it through. Similarly you can't count on him being the same (let alone better) than what he showed two years ago.
Or if the team prefers him to Ruuta waive Ruuta. If no one wants you for free, can't feel to bad about your current team recruiting over you. I'm fine with upgrading them both. If they one of them can beat out Thrun/Muk for the 6th D spot, then you only need to waive one.
I think going into the year with something like Carrier, Boqvist, Emberson, Benning is better than going in with the three currently on the roster. Benning played 14 games. Emberson was a waiver pick-up, played well, but then got hurt. Ruuta will be 34 when the season starts and if he plays well, will be gone at the deadline.
Aside from Walman, Vlasic is the only guy I think is a guarantee to be on the roster after the deadline, and that's because he's overpaid by $6.15M for the next two years. I wonder how Vlasic is in the room/as a mentor. Having a formerly elite (5 years ago) d-man in the room to give advice on stickchecking, positioning, may not be the worst thing for his final year.