The reality is that tools like send-email just... don't really work under the current email oligopoly (since the big providers both heavily filter emails and generally consider IMAP to be insecure). That entire model dates back to the days where email accounts mostly were tied to universities and as a result an emails name had a lot more meaning.

Heck, even for the kernel, send-mail is starting to fall out of practice because it just renders like shit in most email clients. It's a rather dated model.

The pull request flow is the de-facto industry standard, basically all but the oldest git-based projects use it. Not all are on GitHub (since it's proprietary or just straight up issues with GitHub as a company), but even when they aren't, self-hosted git servers like gitea and gitlab are both still using that exact flow.

The examples where this isn't the case are generally rare enough that they're worth more learning as a procedure for that project than as an easily transferrable skill.