I think there are quite a few high profile examples where the fork was successful (egcs comes to mind which eventually became the official gcc, also all the BSD flavours). And even when the fork ultimately isn't successful, it sometimes at least forces the original project to adapt (e.g. ffmpeg vs libav).

E.g. "it's difficult to make predicitions, especially about the future" ;)

PS: of course for this specific project I don't quite understand the reason. The original Bun was largely a line-by-line port of esbuild from Go to Zig, so it's not like the original codebase was a marvel of engineering to begin with...

Same goes for io.js, which got so popular it actually got merged back into Node.js