Tanev has been quietly one of the best defensive defensemen in the league over the last decade. When he played on Team Canada, he drew the praise of McDavid, Gallagher, and Stone as the team's unsung hero.
He could have used a d partner with a nasty side to help deter the beatings in the corner, but didn't get one. Those beatings definitely caught up with him though. At this stage in the team's transition though, moving players (even those as selfless as Tanev) can help to set up the future. Nothing against the guy, as he has been a Canuck through and through.