those of us that are old players who play multi accounts have noticed this trend for a very long time, its nothing new really but still frustrating. it effects everything. including crafting ( much higher % chance of flawless first craft on lower level toons ), event chest item rewards main reward item drop rate, dungeon rewards ( thoe that seems to have been adjusted slightly a few months ago.) and yes, stat card drop rate in void.
from experience, it does not seem to be linked to your current power level, but more along the lines of either castle lvl, or cash spent, now conveniently defined as tier level. but i suspect both play a roll in the overall calculation.