My thoughts were that a rotomould hull would do better when being launched/loaded from a dolly on the rocky beach...
The owner of Trinka told me to be careful with rotamould because it's impossible to repair, unlike fiberglass.
My rotomold Walker Bay is a tough boat, as is my my rotomold Sea Kayak. Both boats are used hard and put away wet. Rotomolding seems to be the way most non performance oriented small boats are going. Its tough and cheap to produce. 30-40 years ago this debate existed in the white water kayaking community. You can't buy a fibreglass white water boat now, rotomolded hulls just bounce off rocks so much better. Some designs where the manufacturers expects heavy beach wear will have a sacrificial keel that can be replaced, rotomolded plastic does abrade, which affects boat speed over time.
I also routinely beach both my fibreglass boats on sand and mud, I dont know how keen I would be on beaching fibreglass boats on rock.
If I was playing around rocks, there is no doubt I would go with rotomold. Same thing with dagger boards vs centreboards. You hit a rock with a daggerboard, the whole boat shudders. You can break the daggerboard as well as the daggerboard housing. Centreboards mostly just kick up when you hit something.
I am not sure which boat would be more stable.
I wouldnt worry about the Cat Rig on the Trinka. Cat rigs may not be as fast up wind as sloops, but they are nice to sail. Tacking means pushing the rudder, no string pulling. Some times, if you have kids in the boat especially, less string pulling is a good thing.