Whether or not those rockstars are also assholes is irrelevant. Mediocre skills will get you mediocre results. You need visionaries, and people who think outside the range of 3-7. Their ideas often fall outside the range of acceptability, and as a result aren't always implemented, but thats where part of the arrogance you're talking about comes from. They may come up with 15 ideas to solve a problem -- none of which get implemented. If they didn't have any self confidence they'd be discouraged (much like you are). It takes self confidence to be on the edge of something, and have the confidence to walk it.
I'm a consultant, and I've worked with a lot of startups. The ones with rockstars do great things. The ones without, trod along, and sometimes don't die.. but rarely do great things. That being said, the world needs 7's too. In fact we need more 7's than we do rock stars. But great things don't happen on their own. We need rockstars to push them forward.