I really think that it is about both. You can have a stellar team with a shitty idea and bomb big time, you can have a stellar idea and a shitty team and you'll do the same.

A stellar team, a good idea, proper timing and now you maybe have something.

A great team can sometimes recognize a bad idea early enough and replace it with a better one. I've seen that happen. Good ideas have a lot less ability to replace bad teams. (Or rather, they can do that just fine, by letting the bad team fail while their competitors win.)