> creating a branch starting at the problematic commit

Code always lives in a context, and when you're fixing a problem that exists in top-of-main the context of the fix needs to be top-of-main, not some commit way back in history. Also if you do it that way, you'd better hope that no later commit also touches that same line.

> I then get people coming to me and complaining they can't merge

A team needs to agree on git practice in advance, and not have one wildcard go off and do their own thing.