IIRC, the oldest was git itself (it self-hosted early on its development history); git, linux, and sparse are IIRC the three projects that have been using git the longest.
It makes vastly more sense to transmit a patch attached to the specific code base state that it is intended to modify: in other words a patch doesn't exist in isolation. Git is great; I'm not saying everyone should use any particular Git-hosting or code review framework. But the fact that the inventor of Git continues to use email in one particular project with many expert and experienced contributors has more to do with their expertise and experience (aka age) than with the benefits of email. I mean look at the reality of these people's workflows: they're using things like Mutt and Gnus to read email locally and apply patches from local email. I get it, I've done it, I've even run a local dovecot for the purpose. It had it's time in technological history. That time isn't now.
There are multiple open source projects that I would have contributed to were it not for the email-based flows (e.g. emacs).
Applying patches is, admittedly, a little more awkward, but it can still be done in two or three steps from thunderbird (including invoking `git am`) and, I understand, some newer email clients can handle this much much better.
> It makes vastly more sense to transmit a patch attached to the specific code base state that it is intended to modify:
This is no longer a problem. `git send-email` (and `git format-patch`, if you prefer to call it directly) has for a while supported a `--base=auto` or the `format.useAutoBase` configuration option to attach the upstream commit ID to the patch. To my knowledge this is currently only to help the maintainer understand its context but there is ongoing discussion of ways to automatically use this information.
Note that I'm not suggesting you use any for-profit company's hosted git product.
ETA: Many forges reintroduce the latter (commenting directly on lines of code), in which case this may not be an advantage depending on if such a forge is used. (But then you're back to using a forge, and needing to open the website to review changes in addition to using git and email.)
It sounds to me, and I mean this quite objectively, not as a personal insult, that you're attracted to the email-based flow not because it is better, but because you just don't want to use a web UI. So since you define web UI as bad, you of course reach the conclusion that the email-based flow is better.
We can quibble about which is more convenient (admittedly I find the former better in this regard, although I recognize that this is a minority opinion), but they are IMO both more-or-less equally viable choices.
It is, however, also functionally equivalent to a pull request, excepting again the need for write-access.
On second thought, let's not go to Camelot, tis a silly place.
You say that like it's a good thing.