Is lighter always better? No. You get to a point where the thing just isn't going to stay on the water. If you had some method of dynamic ballasting, or moving weight to where it needs to be, then lighter becomes practical even at very light weights and big power. Sort of like the unstable aircraft that require constant computer management of control surfaces. Density of the medium and stability are the 'biggies'. Not to mention $$$.
- 'Doc