There is an entire graveyward of browsers, almost all that didn't die are now forgotten.
I think the point isn't that you'll necessarily build a great browser (or LLM), but the experience will benefit you in other ways.
If any were built by teenagers, I’d imagine those teenagers ended up with pretty good careers in technology?
Sure, but I'm sure most of their lead devs are well paid now.
In general C++ work and similar, if not in Chrome development.