I wouldn't say stagnated, he was still good for first half of season, not so much second half including restart, on occasions he has made errors in big games, but it's nothing that cannot be just fixed. He will be playing aside quite a high level of players, unless he's Otamendi from last year just laying on the floor as soon as he's 1v1 he will be fine. He's not injury prone, is quite experienced for his age and has leadership qualities. It's a solid signing on paper I'd say. Also wouldn't compare it to Lindelof, who's stagnated along with all the players who play for scum due to managerial/other various club issues.