Git is a dVCS so yes, it's already decentralized and in that sense GitHub is a mere "starting place" for newcomers who want to checkout the official repo.
However many, too many, use proprietary stuff offered by GitHub on top of it's storage, from PR to wiki etc and those are NOT decentralized and are NOT "free" in the sense of freedom. A FOSS project that depend on GitHub for bugreports, patches, discussions etc is voluntary trapped in a proprietary platform.
We have mailing lists to discuss and post casual patches, Linux kernel work that way, Python work that way, Emacs work thay way etc and all those are not small potatoes projects. We have NO NEED of discourse, GitHub etc if we know how to use good development and user environments, of course we can't develop anything via mail if we are tied to a webmail or to an ancient '90-style MUA monster, we need to know other MUA and other UI to work with (my personal choice notmuch-emacs and EXWM, another populat choice neomutt/*pine and Vim etc). If even FOSS developer lose this knowledge FOSS is at the end.
However many, too many, use proprietary stuff offered by GitHub on top of it's storage, from PR to wiki etc and those are NOT decentralized and are NOT "free" in the sense of freedom. A FOSS project that depend on GitHub for bugreports, patches, discussions etc is voluntary trapped in a proprietary platform.
We have mailing lists to discuss and post casual patches, Linux kernel work that way, Python work that way, Emacs work thay way etc and all those are not small potatoes projects. We have NO NEED of discourse, GitHub etc if we know how to use good development and user environments, of course we can't develop anything via mail if we are tied to a webmail or to an ancient '90-style MUA monster, we need to know other MUA and other UI to work with (my personal choice notmuch-emacs and EXWM, another populat choice neomutt/*pine and Vim etc). If even FOSS developer lose this knowledge FOSS is at the end.