While I don't agree that he isn't ready, I think it would be beneficial for him to stay one more season. He's extremely ambitious and he knows that he's talented, it's the sort of arrogance all great players have. His own aspiration wasn't the same as Gladbach's, when he first joined. They thought they were fighting against relegation, while he wanted to play for the European places. The important thing is that he has steadily improved since then and although there were difficulties along the way, he's probably their most important player nowadays.