a manager is hardly like a player, who improves a lot with time. obviously managers can also grow, but their ideas are already there from the beginning.

I would argue differently. Sticking with the Marsch example he arrived at NYRB ready to be molded. When he arrived with RB he immediately became tutored by Ralf Rangick. Every offseason he would got to Leipzig or Salzburg and work with Rangick or Marco Rose. He would sit in the training sessions of other Red Bull teams and even was a guest assistant. Also in the off-season he would take UEFA courses and did so in Scotland. At Scottish FA sessions he befriended David Moyes and learned some things talking to him. This is absolutely similar to how a player develops, it’s just for managers their training is usually reliant on having a superior capable of tutoring them which isn’t always the case.

It really showed in his time with NYRB because after a few years of this training near the end of his time in MLS it was easily the most crystallized his own ideas had become up to that point and the point in time that he left was the highest level NYRB had ever played under him. The ideas Marsch is succeeding with today were definitely not there at the beginning of his career. It’s not like his style and philosophy was based on a coach he had and even for those where that’s true they still have to develop their ideas for years in practice