I think a good team has a balance of rock stars and junior devs. I don't find it usually the case that a rock star will do 10x the work of a junior dev. In fact they will often do less work - however the work they do is easily 10x or 100x smarter and better for the company long-term. Junior devs tend to work very hard but also can cause a lot of havoc if a someone is not helping to guide them. Many times in fact the work that junior devs do winds up being a mess that the senior has to fix or re-do entirely. Junior devs can also suck up a lot of time from the senior devs, so in fact they may at times be reducing productivity. On the positive side the junior guys tend to bring a lot of enthusiasm and fresh ideas. They keep the senior guys on their toes. And they will grow into senior devs, hopefully giving you a few years of solid work when they reach that point.

"rock star" status to me is somewhat based on age and experience. But in fact some rock stars are young and some mediocre devs are older. I think it has to do more with personality and motivation on the part of each individual.