I don't think the burden of the changing API surface was place on the callers of that API. With core library developers updating their callsites, it meant that

I don't think the burden of the changing API surface was place on the callers of that API. With core library developers updating their callsites, it meant that people calling into early versions of React, never had to deal with upgrading the react version in their package. As a caller of these libraries, it was much nicer to have the React team take care of upgrades where possible rather than having to deal with it myself. Furthermore, there were tons of changes that could happen across the board at facebook that didn't happen at google due to owners files. Lots of people were empowered to make broad changes to the entire codebase which in aggregate made the codebase better. Coming from Facebook, all the systems around owners and readability represented a huge amount of time to be able to make changes that should have been easy. It also left the codebase with many warts that would have been relatively quick to fix locally but a pain to land. Facebook went in the other direction - there were better and better tools for making broad updates