Like other commenters, I agree that grammar corrections are completely fine. Suggesting a different title or subtitle that might attract more readers, great. But when it gets to basically rewriting something to be in their voice with their punctuation preferences (I say preferences, not correcting wrong punctuation), that's when I would withdraw, too. A couple of times over the years on Medium, I had editors "tell me" how to write my story; one of them told me it was wrong that I didn't offer any advice at the end. Well, I wasn't writing an advice story, thank you very much. Having just completed a memoir writing course, I've learned about what is helpful feedback and not. Anything couched with "should" isn't helpful.