That's true. It's never a sure bet when someone has success on one side then can't duplicate it somewhere else. Just look at Joss and the avengers. He goes to DC and can't recapture the magic with justice league.There is no indication that he would have been able to replicate that again in the MCU.
One thing I do know for sure, he is no Feige. So I don't know how he is going to turn DC Studios into Marvel Studios as Zasie is expecting.
What Feige did with the infinity saga might just be the greatest achievement in cinema. I'm not sure anyone can fill those shoes. I don't think he needs to, he just needs to chart a course and plan it out. Can he do that? I'm not sure, but it will be fun to watch.