I like the player, and the direction of the defense a lot. 8 year term is hard to swallow, but the last 2 years are a very easy buyout if need be. He'll likely start next to Werenski which I think is fine, but then when we're actually supposed to contend, Severson will be the perfect 2nd or 3rd pair RD. All teams that go far in the playoffs have a D-man of Severson's quality on one of the bottom 2 pairs.
To add, Babcock likes to play a fast transition game with stretch passes, and as I understand it, both Provorov and Severson are very good in those regards. I'm also less concerned than others with their defensive abilities. Provorov's defense I am actually 0% concerned with. At his best, he's solid all over the ice. Severson has been playing in a high-risk high-reward system, which will likely continue here, but I think he's probably more solid overall than he's given credit for. If he makes an occasional mistake, that's fine for now because it's not like it'll be more frequent than what Peeke or Boqvist were doing.