I have more than once subscribed just to report a bug or send a patch because the mailing list rejects emails from non-subscribers.

Edit: Btw, yes I have done the periodically-check-archive thing in the past, thank you. Hated it. Also missed a response once because I forgot to check and replier didn't CC. I realized like a month later.

Even then, you’re free to opt into daily digests if you’re a subscriber. The message ID allows you to reply to individual messages and threads nonetheless.

It is unfortunate that there are poorly-managed projects with poorly-managed mailing lists (just like there are poorly-managed projects on Github), but sourcehut at least requires a properly-managed mailing list, and I think you should evaluate this workflow on that standard. Tell poorly-managed projects to move to sourcehut, if you want to fix this issue.

Presumably you'd be interested in any feedback, and not everyone CCs the original author in their reply.

Reply-to-all is the standard policy on most mailing lists. Especially on -devel lists since you'll pull in (CC:) people outside of the mailing list (cross-project) into discussions from time to time.

I know more than one occasion where that has gotten an angry reply.

It's also not the default in many clients. It's tedious and error-prone.