That’s not to say that Github pull requests and the like are perfect (far from it) but it’s undeniable that they smooth the process quite considerably and make contribution far more accessible.
1. One account for manifesting your chosen identity, which you likely already have.
2. One common way of getting the source code and sending diffs/patches (read: PRs).
The workflow is quite similar, in the abstract. But GitHub and friends solve important pain points.You also have an email address, so. You need an email address to get a GitHub account, so technically it's harder to set up GitHub.
2. One common way of getting the source code and sending diffs/patches (read: PRs).
This is built into git. Don't need GitHub for either.
Perhaps the last argument I have is that I've heard a number of times about moving a project to GitHub (for example: the Go language or Vim the editor), but decidedly less often one hears of projects moving away from GitHub towards older forms (such as the wonderfully documented https://gcc.gnu.org/contribute.html). Despite the great documentation, I'm somehow not drawn to hacking on it to fix a small glitch, due to the overhead that entails. Mind, some of that overhead would be incurred just once, as it is general to the mailing list approach to collaboration. That, I believe, is another advantage of a project being on GitHub: for almost all projects there's a standard way of sending your patch: make a pull request.
About your counterpoints:
1. True. I was thinking of the bug trackers many mailing-list oriented projects have, which often require creating accounts just to file a bug. 2. I was more referring to things like (1) where to find the clone URL and (2) how to send a patch (the make a PR button is always the same).
Removing friction (even small frictions) will enable fishing for the long tail of small fixes. On the other side, I do not believe large contributions are greatly affected by the differences between these systems.