Not necessarily. With young startups, the only available position for a role is often "Founder". A developer could simply want to work on a project and see where it goes, and the only way would be to become a founder.

In general yes. But with YC, I get the feeling that there is a push for founders who at the very least won’t actively shun the limelight if required.

Yep: There's a reason a bunch of YC founders appear every year like clockwork on popularity lists like Forbes 30u30 ...