Negatory, systems states change, which can affect rare allocation (people keep arguing it doesn't, despite a clear correlation that it apparently does; that may be new(ish) but does seem to be a thing). If a system with rares sees a state change to boom (or potentially expansion) then the rares can spike in allocation count.
Rough numbers look to be about a trillion and a half worth of credits (give or take, depending on faction) in discovery/ exobio to hit rank 100. So in other words, Frontier reacted to the (fractional) number of players who haven't turned in expo/ bio data for 2+ years, set the return based on that, then invalidated any meaning by setting a 'from' date which solved the original issue, without really needing to offset the payout (since everyone would be starting from scratch).
Frontier has made a good start with Ascendency and some of the improvements, but the exploration merit thing is just nonsensical. It's like a few different people implemented 'fixes' without talking to each other (and didn't use a calculator).