Mary

Again your quite right, the wave is the boat for this task, but I would say that of the three reasons you justify it, small, heavy and underpowered, the two that really count are small and underpowered, and of these the most important is underpowered.

To get back to the original question, I can still think of no benefit to having a heavy boat, but if someone was convinced, there is nothing to stop them strapping a load of lead onto a light boat to make it heavy while they are learning, then taking it off when they want to. You can't take the weight off an already heavy boat.