The tricky part of the enrgy return equation is that it will affect different types of horses differently.
Within the same race a track may return X amount of energy to Horse A, and a completely different amount of energy to Horse B. Primarily dependant on the duration of time the horses foot is in actual contact with the ground.
Because the resulting energy return occurs at different times (in relation to the initial impact) a horse whose foot is in contact with the ground for .X seconds may get a low percentage of the energy return, whereas a horse with a different duration of foot to ground contact may be getting the optimal amount of ER.
At some moisture levels, speed horses may (on the average) benefit, on the assumption that generally a horse running a 22 flat 1/4 has foot2surface contact for a shorter duration than a 24 flat 1/4 runner.
Again, this is just a generalization though, as some horses run a 1/4 mile in fewer strides than others.
Bottom line is that it is without a doubt true that the track surface, and it's associated variant changes from race to race, and probably from lane to lane, due to moisture content.
But in recognizing this, you must also recognize that the same phenomenon does not have consistent effects from horse to horse. The science that proves the race to race variation does the same for horse to horse variations.