Personally I think it’s so much better than PRs (not that I don’t think it can’t be improved), but to each their own I suppose. I’d also be happy if GitLab had an HTTP endpoint you could submit a single patch or an archive of patches to, or something like that.
(Apparently it does support submitting patch files directly. Via email, but not in the git send-email format. Weird. Will have to try it at some point.)