Fair, but my confidence in it stems from the giant community around Next.js. Zeit, a company with a good reputation among developers, works on it full time. It has contributions from other big-name OSS contributors and big companies (Netflix, Hulu, Nike, Ticketmaster, Jet, Auth0, Marvel, etc.). It's definitely a liability if it were truly just one individual developing it, but I suppose it's more that there's a small core of facilitators, with a giant OSS community around it.

As said elsewhere, I mostly act as a curator of a very large effort of hundreds of individuals. The project was actually co-created by several other people who work on infrastructure at ZEIT (e.g..: Naoyuki Kanezawa led all the initial releases, designed important parts of the framework, Arunoda Susiripala contributed the test harness and key build pipeline infrastructure, and so on).