Regardless of clip less or platform, I have observed that many riders, children and adults, do not know how to start from a stop. If you don't know how to start smoothly from a stop it doesn't matter what kind of pedals you have. There is also a correct way to stop so that you are smooth and are less likely to fall. During last Sunday's Portland Parkways it was surprising to see how many people don't start smoothly and wobble all over.
I am not saying that this describes you, however you mentioned not being great even on platform pedals so it got me thinking about the stops/starts.