I'm not sure that there is a difference in the long term benefit to the development of the athletes either way. While I certainly see your point, you could also argue that it would be easier to learn technique with a smaller flyer, then move to a larger one later. This is much the same principle as learning a tumbling skill on a trampoline/rod floor, then moving to the spring floor.
In terms of the current scoresheet, I don't even think it is even close. All else being equal, difficulty scores much higher. The size of the flyers does not seem to make a difference to the scores. In other words, on the scoresheet, putting up a 130 pound flyer in a full up stretch gets you the same credit as putting up an 80 pound one in the same skill - even though putting up the 130 pounder is usually much more difficult. We could certainly debate whether or not that is the way it SHOULD be, but that is definitely the way it IS.
Yes, I know that some heavier flyers are easier to put up because of technique differences. In general, though, lighter is better. This is only true to a point - as an athlete starts to either lose too much weight (or lose it too fast) to the point of being unhealthy, the loss of technique and strength hurt far more than the weight difference helps.