You'll be surprised, I think the best codebase I ever contributed to is the Rust compiler, which is being built by a huge distributed team.
Despite it being complex and me being in there for the first time, I could quickly track down a bug in the parser and fix it. As a cherry on top the communication around the pull request was top notch too.
I’m not trying to say it can’t be good despite that factor, but if the rust compiler were written by the top 4 contributors sitting in the same room, it’d be even better (and possibly not finished yet ;) )
It took my company a team of 8 fully-remote devs to fix the clusterfuck of a codebase that the "4 guys in a room" (the CTO and early devs) built up with spit and tree bark,.