I used to feel that if a club had world-class players, any coach could manage that club and get good results because the players knew what to do on the pitch to win a game, but after I had seen how different coaches had failed to get good results in clubs that had world-class players, I agreed with you that getting a good manager is very important for a club that has world-class players to flourish and win matches easily.
That was 10 years ago, the world has evolved. Football is beyond having the best player in the team, it is now about tactics, having the right player to give you the exact result in your formation, game structures and game plan. When you lack these things in the club, no magic can be done to keep winning. Real Madrid has the best players in the world, but they fail to win the highest competition last season. The manger becomes very important because he will be the one to bring all of these things to the table for the team to replicate in the field.