80% is a good ratio. My acceptance rate for standard assets is near to 100%. It's only when experimenting that I get more rejections than usual, mostly then on the commercial appeal or non-compliant image.
A rejection rate of 50% is still good, if you are a.beginner, you could even live with your first 10 assets to be rejected, if you will get lessons learned from those rejections.
Most people are throwing in anything just to see what happens. When I started, I selected my best shots first, giving me a good acceptance rate. Only then I experienced some setbacks because I started with more critical assets, like counter light photography.