I think we might be misunderstanding the weight thing as lighter is always more optimal and not necessarily what is the optimal weight of a board (given the conditions it's shaped for)
Having pro light boards can increase response, and I think are generally better for performance, but with too light boards, you can lose some drive and momentum.
Having an optimal weight for a board is an interesting idea, and may have more substance to it than you'd think.
Put it this way, if you have the same volume (same blank or type of foam) and same glassing schedule on a several shapes, wouldn't those boards all weigh the same?
you know how you can feel a board off the rack and just instinctively know it will work?