They' re telling it true, Capt Ray. You' re not taking bow efficiency into account. A heavier arrow takes more of the energy from the bow as it begins moving and accelerates on release, so that arrow absorbs more energy than a lighter arrow does. It' s not moving as fast as the lighter arrow, but it' s packing a bit more punch. Usually not more than 3-4 ft lbs though.

You can shoot different weight arrows out of a given bow through the chronograph, punch the numbers into your calculator and plot the graph. As arrow weight goes up, KE goes UP, speed goes down. When you find the point where the two slopes on the graph cross, that' s the theoretical point where you' ll get the most KE at the flattest trajectory. Do you want flatter trajectory than that? Then you drop arrow weight and trade off KE for speed. You want more KE? Then you add arrow weight and trade off trajectory for KE.

It' s all so simple...