Even if it were true, in real life it doesn't tend to work that way. You really can't shoot the same arrow from a bow with a 4" longer draw. Also, longer arrows have to be stiffer, and usually heavier and slower.

It also doesn't account for differing power strokes from brace heights being different. Is there that much difference in arrow speed from a guy drawing 28" with a 7" brace compared to a guy drawing 30" with a 9" brace, where the peak draw weight is the same?

I would say that the potential for an equivalent speed would be there is the longer draw person, could shoot the same weight arrow accurately (or didn't care about accuracy or penetration).