Pretty much lays out the reason the Sabres moved him. As expected, the pricetag was never going to work for Buffalo's mix as a sort of 2a/b guy with Cozens. Easily palatable for the way he slides right in as a clear #2C for the Avs and their team structure though.
As much as Mittens seems to have rounded into an alright #2C...it was just not working with the mix down the middle for Buffalo. And you can't really spend $7.1M on both of Tage and Cozens, then also go out and spend another $5.75M on another guy competing for more of a Top-6 scoring role as well. Not if the overall mix of Centers isn't getting it done. Specifically...if none of them are any kind of real "matchup Center" and there isn't really a lot of great PK ability amongst them. Puts an unreasonable burden on your #4C to be an absolute PK and shutdown monster.
Moving Mittelstadt allows them to go out and try to find a much better "fit" at #3C who can play a matchup role, lead the PK effort, etc. Easier said than done...but at least they have the flexibility to do so, and a good asset in Byram to work with in trying to get there. They don't have to deal with an extremely expensive $5.75M + $7.1M = $12.85M 2a/b scenario that isn't addressing the most pressing needs from one of those two "middle-6 center" roles.
Also seems to be a great fit for the Avs and Mittelstadt though. He's good enough and fits with their system well enough to hold down that #2C gig with the wingers they have and what they need out of him there.
Continues to look like a rare "win win" trade. This contract is just part of the "win" for both teams. Buffalo doesn't have to deal with an expensive pair of middle-6Cs that aren't getting it done. Avs get a reasonably enough priced #2C for their own situation. Cool beans.