> the rest smell like an antifeature to me in fact

I believe without it you can't push to a PR? As a maintainer, I find it quite useful: if a PR is essentially fine but needs a minor/trivial edit (typo, maybe add a few lines of documentation, extremely minor code style changes) then I typically just make then myself as I don't want to bother the submitter for that. Faster and easier for me, faster and easier for them.

Either way, of course all of this is possible without the "gh" tool – no one claimed it's not, – but it's a lot easier than "stick these commands in your git config", especially for people not well versed in git.

Of course you can. You can always use the long form, or set it up explicitly - I sometimes do that too as a maintainer. Setting this up by default when you just want to checkout means that it's easy for you to push things to other people's repos by accident.