I don't have strong opinion against mail-based contributions (I suspect they are perceived as less beginner-friendly by newer contributors who have grown up in the web-interface-based-world, but that's a discussion for another time). The problem here is that a select group of contributors can use a certain contribution procedure (here: Merge Requests), and external contributors have to use a different approach (email or issue-based), or ask permission to use the first-group's approach. In this setting the second approach is *objectively* second-class, and this difference objectively sucks.
There are other places that host Gitlab instances without this restriction.
(If you are interested in hosting a web platform for git hosting, I'm told that gitea (
https://gitea.io/ ) is much easier to deploy than Gitlab.)