The amount of data the RC / goggles have to send to the aircraft is minuscule compared to the video feed sent by the AC, so can be done at lower bitrates = less power needed for same range.
thats true to some point, but hard to say by how much - at some point if the SNR is too high, the control link will be unusable/unstable - and it'll fail.
... also why if it is asymetric, is it only on the 2.4ghz channel?
all that said, it doesnt affect me , where I fly , increase power does very little to increase range.
basically, if a mountain gets in the way... its blocking the signal, otherwise, even CE power will go a long way on 2.4.
I guess, in highly rf polluted area it would help, but then you'd use 5.4, which is spec'd the same on both aircraft and googles/controller.
who knows, seems like an oddity, perhaps there is logic, perhaps there isnt