I don't understand this community. I thought mangadex was like mangago where there is a single version of each chapter so if someone uploads a chapter, it is proper etiquette to not upload another translation of the same thing unless the previous translation is auto-translated and very bad. Then it came to my attention that mangadex is specifically designed in a way that a chapter can have multiple versions by multiple groups. The fact that the option exists means the website encourages multiple uploads since it's implemented in its core. Of course, if someone takes the same scans from someone else and reuploads them under a different name, it shouldn't be done but any other case is perfectly fine.
Personally, I don't see anything wrong with this. I don't even mind if on websites like mangago, a group B uploads before another (group A) even if group A has uploaded more chapters before. Some groups sit on chapters for 20+ mangas and take too many projects and then get angry when someone else starts working on 3 projects and does so faster than them. Why is that an issue ? You don't have the copyrights or any ownership to this. Translation is a hobby and no one should be denied it just because you made a "reservation" and then got busy with something else or even if you didn't get busy, it's not your thing! If so then one group would just upload a single chapter of 10000 mangas and forbid anyone else from uploading any updates while they take months and years to add new chapters. That's not how this works. I used to translate around 8-10 years ago and it was much less problematic back then. Now it feels like groups are ganging up on each other. Do your thing and let others do theirs