In my experience you can always count on a team to do in just an year what a single developer takes an entire week to finish.
What absolutely does not mean that teams are useless. But that choosing the correct size and composition for them is one of the most important decisions for a project (right there with "are we solving the correct problem?"). And "more is better" is a completely wrong way to decide on it.
Also, this doesn't make that one developer a "rockstar" or whatever else you call it.
The best teams do the most because they have the most trust. The worst teams are usually spending time paying down technical debt, or busy generating it to meet a deadline.
Same goes for "rockstars", only its easier not to "lose your groove" if there are fewer people pinging you. You still run the real risk of two "rockstars" playing out of sync, and causing a mighty mess down the line.
What absolutely does not mean that teams are useless. But that choosing the correct size and composition for them is one of the most important decisions for a project (right there with "are we solving the correct problem?"). And "more is better" is a completely wrong way to decide on it.
Also, this doesn't make that one developer a "rockstar" or whatever else you call it.