I’ve never claimed Mainoo won’t progress, he quite clearly will and ten Hag will continue to make him a key player in his team.
However, if you re-read my initial post, what worries me is us ironing out very positive traits he has naturally in his game that will be ruined by the style of football we play. Ten Hag has on numerous occasions admitted that what he wants his midfield to do is play transition football. We averaged 50.4% ball possession per game in the league last season (joint with Fulham). By being a side who do not value heavy ball retention and instead instantly look to play expansive and progressively, we will forego Mainoo’s ability to play in possession. All whilst he’s still in the formative years of his development where young players absorb traits and habits which shape them for the rest of their careers.