We do our best to help those willing to work with us. I've had hopeless articles gradually polished into shape by writers who had a strong voice but perhaps a weak grasp of grammar. If they are willing to listen and learn, we can overcome the obstacles.
There is so much superb advice here on Medium on how to write well, how to tell a good story, how to follow the rules, how to format the thing for best chance of curation etc.
And so many great examples. Honestly, if someone spends a week or two reading what Medium has to offer, and takes it in, there would be no need for an editor at all.