Gelcoat scratches as well, you just can't see it on a white hull. That's whey most glass boats have white hulls. Because most stripers are natural finish, the scratches are white and it shows. Epoxy is harder than varnish and it's the varnish that scratches easily. It's just the sad physical facts of the strip building process. After a while you will get immune to it and varnish your boat once in a while and don't worry about it. Use obvious care with your landings. If it's a rocky landing, most strip boat paddlers stop just short of landing and pick it up and carry it on to shore. There is no chemical surface made that will glide over rocks, the closest might be the waxy surface of plastic boats.

This is one of the reasons I put two layers of glass on the bottom and plenty of epoxy.