if you are educated in the system, you don't need American Idol, you will get where you need to based off of how much work and effort you put into it.
you remember DJ Sammy released the song, Heaven? people thought that he sung it, when really it was Yanou, the female vocalist, did she get recognition, barely... DJ Sammy was making the money, not Yanou entirely. to this day, people don't even know who Yanou is, get the point?
Tess, her songs hit top charts. people don't know her full-real name. they just want to know what songs were released by "Tess."
it really depends on what you are looking at, popularity or one time hits? legends, it'd be something like Britney Spears or Backstreet Boys. Their image was very good, their image now, I would rather not contest; you can fill in the rest.
as far as American Idol goes, they're singles. teams that consist of multiple singers or members will often times perform at places where they can be recognized or just do it for fun until some contractor who likes them will help them get into the business. how big and far they get will come if people like them and the advertising and how well they demonstrate aggressiveness in the market by showing themselves more in public rather than hiding their faces.
DJ trance artist, ATB, his music I think is great, but there are people who don't even listen to his songs all the way through, sometimes just used as minor fill-ins to complete mixing for concerts and clubs. you could be popular by name even if your music sucks, Christina Augulera, her music I think sucks even though she's super popular.
american idol is a stupid show anyway, people just watch it because they can't realize that talent exists outside of the television, lol