You got the point perfectly. Margaret Mitchell's writing career is measured by what she produced, not how many years she worked.

In my experience quantity leads to quality (like Bradbury said, "in quickness is truth"). On top of that, the more you produce, the more you have a chance to land a hit like Margaret Mitchell did.

I'm not sure there's any blocked writer for whom more perfectionism is the cure. Mitchell wrote 3 books (unpublished) before Gone With the Wind. Creating, experimenting and shipping your work is the name of the game. The more you create, the better you get at your art.