Tbh, Puig situation is not really the problem of Koeman. Koeman just doesn't have it. He's a mediocre conservative manager, inferior to Ernesto Valverde. You just don't want that for anything more than a stop-gap season.
Being a club legend doesn't have anything to do with his skills as a manager. His value as Barca's manager is on trial here, not his career and influence as a player 25-30 years ago.