patronus said..
Some brands' blurb and reviews say pumping to get flying can be improved by reducing the pressure of wings, but doesn't that lose energy as wings flaps about rather than drive forward and lift?

if you are a lightweight rider or have a decent technique you do not need to do so.
But if you are a heavy guy or lack a little in pumping technique you profit more from a deeper profile of the wing.
But you also loose some control as the wing starts moving the draft earlier, so when the wind picks up th wing feels heavy and the draft is moving. Upwind angle will also decrease.
The deeper draft will therefore help you, when directing the board to a downwind course, gain more speed in a passive way like a spinnaker.

figuratively speaking....

I think it depends upon the wing. Reducing the pressure on an Ozone Flux appears to improve low end as it adds a bit of camber without too much distortion. But, my old F-One Swings had terrible low end unless it was pumped up hard because it flaps and distorts so much.

A low pressure wing may have more low end power, but I can physically pump a stiff wing faster with my arms in a circular motion and thus create apparent wind. So I vote for a stiff wing.