I would disagree with that. Github shows a lot of the benefits of centralization, where they get network effects from forks and pull requests when these do not

I would disagree with that. Github shows a lot of the benefits of centralization, where they get network effects from forks and pull requests when these do not have to cross git server boundaries. Using external services in your build process has little to do with centralization. People that do not realize that having an external dependency in there is bad, will also not realize that having two or more of them is bad. That does not mean that you are not allowed to sync stuff in from github, but your release should be buildable without internet connection from local data.