Besides, it isn't "self-hosted basement Git server VS Github". There are plenty of other large and reliable forges out there, such as GitLab, Sourcehut, Bitbucket, or Codeberg. Considering how many people - from individual devs to major open-source projects - are abandoning Github, launching a new project in 2026 which only works with Github is a rather odd choice.
It doesn't even make sense from a technical perspective. Git has a standard protocol it uses for cloning repos. You have to go out of your way to make it not work with other forges. And if reliability is critical, surely you'd just mirror it locally? Heck, why not make use of Git's inherent distributed nature and allow defining multiple upstream sources? Integrity is already handled by the commit hash itself, so it doesn't matter if you fetch that commit from Github, GitLab, or some guy's basement server - just take whichever one happens to respond the fastest.