First we have to consider how light is too light or what is, light enough. I am not sure we know that yet But assuming we create a board light enough (whatever that is in a given era) and that this board also has sufficient volume and surface area to function properly (whatever that is in a given era) then, where the weight in the board is distributed, can be played with and the best location sought out.
For example, if a super light board is say… 4 pounds and that is our desired target weight but current super light boards are say 6 pounds. Then we have to find a way to shave off 2 pounds. Maybe we can’t get 2 pounds off the board but we can get 1 pound off. In that case, we need to figure out where the 1 pound should best come from. Nose, Tail, Fins, Center, Perimeter, or all over equally, etc. If we choose correctly, we my be able to improve the ride and performance significantly even though we were only able to remove half the weight we hoped to. In other words. We could improve the board not just by making it simply a pound lighter, but by making it lighter in exactly the right places.
On the other hand, if we can create a board that is say… 3 pounds and our target is 4 pounds we can then choose where to place that 1 pound extra weight for the best gain in performance.
We of course aren’t considering strength here as a variable. So for the sake of discussion, all these imaginary boards are going to be strong enough, and shaped properly so that we can isolate the location of weight and not get hung up on other issues and be unable to discuss this weight issue in depth.
So… assuming we can put this 1 pound where we want… where will we put it? To consider this we have to remember that we have a board that is way too light by at least a pound. Since this is a rare occurrence, everyone who wants to dive into this discussion has to make a major adjustment in their thinking to take the rare position of an otherwise excellent board being too light. Once we are adjusted to that norm we can talk comfortably about where to add weight. Rather then where to remove it. As one would want if they were still looking for lighter being the ultimate goal. Which it may be. We just have to dismiss it here for the sake of discussion as we have to remove it as a distraction if we are going to consider where weight should be best located.
As you noted, removing weight from the areas in front of the rider is fine if you have a board that is generally too heavy in the first place. That is the norm we are accustomed to, so Carpers comments are not unusual. Swing weight as you called it, can be a big negative, especially in small waves. But in larger waves a board that doesn’t have some degree of weight forward of the rider can suffer from loss of projection, momentum and authority. Remember, there are a lot of personal preferences in how common boards ride. Few have ever ridden well shaped boards that are too light and then had to choose where they were going to add back a little weight. Few have considered this challenge let alone worked on it.
In addition to the effects of fore and aft weights noted above. Perimeter weight can slow rotation from rail to rail (or around the center) and provide a more solid feel and stable ride while centered weight will enhance rotation but may leave a board feeling a bit squirly or twitchy. Of course, all these will work in conjunction with the shape of the board etc. Like a wide board with perimeter weight and a concave bottom and big fins with too little cant, ridden by a short rider with small feet may feel nearly impossible to turn. But lets not go there, lets stay focused on finding the best location for weight.
Those who know a bit about airplane design, yacht design etc will recognize the importance of weight and where it is located. This is generally referred to as the “Center of Gravity” (balance point). The CG is the average location of the weight of the object within the object, though sometimes the CG can exist outside the object like in a boomerang.
Because a surfboard, in flight, is a combination of the board and rider, the CG will vary in its location. But when loaded in a turn and then released into a trim, the CG of the BOARD can be more prominent if not dominant. In trim, in good waves, it seems to me that the CG should be just in front of the riders CG. This may not be true in small waves where one is just wagging the nose back and forth to look like they are actually doing something! When snapping off the lip or top turning, the CG of the rider will be dominant and must lead the CG of the board. Especially if the velocity is decreasing and the board is not accelerating such that its CG is driving the turn like you can sometimes do in large, powerful waves when turning in long power arcs.
Because we need to alter a boards track and direction it isn’t appropriate to have a heavy nose like an Arrow would. But neither is the opposite true as we often need to project and drive the board forward like an Arrow from time to time.
I will stop here for now as I am sure others have much to add.