Well, this really depends on the startup and what stage they're at. At the early stages, where it's just the founders, it's probably for the best if the founders are generalists and can handle almost anything. Once someone lands the funding/revenues to actually hire, then of course it makes more sense to get specialists at some point.

But even then, making your first couple employees generalists doesn't sound like a bad idea to me at all. Of course, this is all speculation: I've never hired anyone, hence everyone should ignore whatever I say here. But it's definitely easier to work with people who can pick up new stuff quickly, and a generalist is usually that type of person in my experience.

I don't think a rockstar is someone who already knows everything so much as someone who can learn to do whatever is needed at any given moment. And honestly, that is the kind of person you need at a startup.