I agree with you about the project being a joy for the developers.
But as a user, in no way I would rely on a browser started in 2020 written in c++ (or in zig, given other comments about its security characteristics). Keep in mind that gecko/webkit were written initially in c++ because c++ was the best language available at the time for these projects. This is not true anymore.
The beauty is when you build your own OS with it's own desktop environment, and browser and tools from scratch you can use the language you feel is appropriate. Would you write a brand new project in a language you don't feel comfortable with just because it is perceived as "safer"? Especially when the project was just for fun, and really to help the creator get through some tough times in their life. Like he didn't start the project to compete with mainstream OSes or browsers. This is just a terrible take especially considering you probably use an OS written in C and a browser written in C++.
But as a user, in no way I would rely on a browser started in 2020 written in c++ (or in zig, given other comments about its security characteristics). Keep in mind that gecko/webkit were written initially in c++ because c++ was the best language available at the time for these projects. This is not true anymore.