For once i actually think it's the opposite. The longer he's been out the easier some are willing to just discard of him. He's the best midfielder we have at getting stuck in and protecting the defence while also being good enough on the ball to be part of our best midfield when everyone is fit.
It took until early February last season for Rangers to concede a goal in the league when Jack played. 16 straight clean sheets. You can tell when watching the matches that the defence are far more comfortable when Jack plays and the numbers back it up as well. Since last season we have kept a clean sheet 79% of the time when Jack plays as opposed to just 46% when he doesn't.