I've pondered the low/high flange question for many years. I suspect the supposed stiffness of a HF hub is because the spokes are assumed to form a broader triangle flange to rim to flange.

But consider a spoke running vertically upward from hub to rim. When you enlarge the flange you don't increase the at-rim angle of the triangle by moving the flange end upward, and you don't substantially shorten the spokes. Instead, the flange end of the spoke is moved forward or backwards, not upwards. Of course this is because the spoke emerges more tangentially from the flange than radially. That vertical spoke, when viewed from directly in front or behind, does not change its appearance, though the bottom end is slightly closer to you or further away. So the only thing that changes structurally is that tangential forces are more easily transferred from hub to spoke. It might make a different on the rear wheel, but on the front it matters very little.