In my experience, Overleaf is actually awful for collaboration. Maybe my workflow is weird, but I tend to look at the diffs after my colleagues make changes. Also, we mainly use pull requests to add to our papers. This way, everyone can see and comment on changes.

This kind of workflow is not really usable with Overleaf. Overleaf uses Git in the background, but every commit is named "changes on Overleaf" and the individual commits do not really make much sense. In addition, everything is immediately put into the master branch and there's no way to summarize or group changes (like with commits and/or pull requests).

My next problem is, that Overleaf just uses latexmk so if you have some code to generate graphics or tables, you have to compile and add them manually all the time.