The players are collectively underperforming because of an incompetent manager, not the other way around. If it was one or two players underperforming then it would be easy to identify them. If it’s the entire squad then that’s 100% on the manager.That no matter what Rangnick does, the players won't make the required effort. They are lazy and difficult to work with.
Rangnick hasn't done well, but some fans are giving him too much stick.