This is actually not correct with the current weight of BBs we have. A .43 and a .36 at .9J (which is 212 FPS and 232 FPS respectively) will both travel about 210 feet flat, the .43 is actually a flatter trajectory than the .36.Correct.
What he is saying is that there is a point to where the heavier bb's will be a disadvantage. So heavy bb's are good to a point and then you may go over the optimum point and they may be a disadvantage.
If we get into .66 then this becomes true. a .66 at .9J (171 FPS) will only travel about 150 feet. The reason is that the hopup takes effect pretty much straight from the barrel instead of at a distance because of the slow speed.
But since we don't have .66 yet, using .43g BBs is 150% time better than using any other BB at the same Joules.