Uh, it's definitely a bad idea to be concurrently developing on the same branch for a lot of reasons, large org or not. That's widely considered a bad practice and is just a recipe for trouble. My org isn't that huge, and on our team for our repo we have 9 developers working on it including myself. We still do MRs because that's the industry standard best practice and sidesteps a lot of issues.

Like, how do you even do reviews? Patch files?