[bhaak]

It's not about usability for newcomers (a mailing list is really not ideal for them) but usability for regular contributors and especially for lengthy discussions.

Call me old fashioned but there is no better way of discussing stuff online in an asynchronous way (OTOH video calls are better, but face to face doesn't scale) than a threaded medium. We don't have a better tool to manage threaded discussions than what mail clients (or Usenet clients but they are almost identical in handling).

Linear discussion forums (which GitHub issues are) are just inferior.