Issue tracking is optional, if you disable it users wont be able to fill issues. You can easily ignore release system (by not using it) and I am not sure what you mean by authentication. As for pull requests, it is reasonable to expect contributors to submit them wherever your readme points to.
I don't mean to say that gnome should use github, I think that it is overall better if there is no single dominating company for open source. Just that organizing so that github is git hosting only is not that hard.
The whole point of the migration was to consolidate things to make onboarding new contributors easier. If they only used the git part of github, it would be little better than their existing cgit setup.
I don’t understand where in that comment you believe I suggested that the Gnome team should have chosen GitHub. Most likely because I made no suggestion.
Please try to be more careful with how you approach reading comments.
Make sure you also tell your users not to use GitHub's comments, issue tracking, pull requests, release system, favorites/watches, or authentication.
So you're suggesting that the new home for the GNOME project's code be GitHub, without the GitHub.