Suicide ball is the way we played last year when we were conceding 20+ shots per game because we were playing a 1 man midfield. As I've already pointed out to you, as have several others, our terrible performances came both whilst he was in the team and when he wasn't. Performance levels were independent of the players because the formation and instructions were mental.
I think, without disputing that we were too open last season and that we had obvious issues in tighting up midfield in the majority if games, that your argumentation here is too simplistic to make use of.
After all, the truth is also that we played quite a lot of games under Ten Hag with more defensive control as well. Many of these were in the season Mainoo didn’t play. Some of them had tactics more similar to what we now saw under Van Nistelrooy, with more compressed team, fewer comitted forward in the high press, and a more conservative pivot.
Also, most of us have really only seen Mainoo play magnificent football under two managers, both much maligned, incidentally. If they have exposed him, they are also the ones who has allowed him to shine. To the degree were many think of him as one of the worlds most promising teenagers.
The argumant that Ten Hag was a lunatic and nothing from his reign can tell you about a players capabilities, simplify things as to be completely black and white, and obviously wrong too.
Mainoo is my favorite United player atm personally, yet I eon’t be surprised if he will have a few seasons in and out of the first eleven now. He has enormous potential, but it has to be eked out, and he has skills already top notch, but is inexperienced in how to make the most of them. His weaknesses will tend to leave a team exposed while he learns, defensive awareness and positioning are two of them for me, foresight and in gameplay and hunger for dictating things two other things to develop.
Garnacho is in a similar position, whereas Mainoo has better allround technique, overview and strength, Garnacho has a seemingly immense hunger and confidence to me will ensure that he will develop his game one way or another.