First, I would put water-skiing, like you. Then, for the similarity of this sport, I would say that snowboarding could be the second less dangerous extreme sport.
In the third position I think like you, ice hockey, because they go very fast and they can slip and, for example, fracture their leg.
The fourth position could be occupied by the white water rafting.
After that, I consider dangerous rock climbing. I think it looks like a very dangerous sport, but in fact you are well secured with ropes.
Following to these extreme sports, the ranking continues with scuba diving, it's a beautiful sport but could be dangerous because you are exposed to dangerous animals.
Finally, I