There is certainly some gain in performance with higher draw weights, but I agree that the increased performance does not stay in line with the added weight.
Long story short, I have several sets of limbs for my favorite recurve, including 55lbs, 60lbs,
68lbs, and 82lbs.
There is a noticeable performance gain from 60 to 68lbs, and only a slight gain from 68 to 82.
The gain from 55lbs to 60, is very slight. Changing the limbs from 55 to 60 or vice versa, cannot be determined by watching the arrows fly.