Open-source can be deeply rewarding and some people really pour themselves into it. I think assessing one's level of investment falls to each contributor themselves, and I wouldn't condescend to tell a stranger that they've made the wrong decision about that.

That said, a lot of people in the Nix community go above and beyond what could reasonably be asked of them by others, and it probably does put them at risk of problems including burnout. I'd be interested in research into emotional well-being and F/OSS involvement in general, because it could be really valuable in informing strategies for building F/OSS sustainably and even personal advice for staying balanced.

At the individual level, though, concern about this kind of thing is best left to people who don't need to look at metrics related to VCS activity to tell if someone is taking a hobby (or job) too far— trusted, close relations: family members, old friends, life partners, dear neighbors, etc.