Unless I am mistaken (which is very possible), there are two “rares” for every two blister packs. At the same time, there are 13 “common wackys” and 15 GPKs.
If that’s correct, it means a given pair of blisters would have 20% of the “rares” and 13 out of 45 (around 30%) of the commons. So the rares don’t seem much rarer.
Depends which blister you buy.
so far, the yellow header packs predominantly have a Wacky mystery, and the red header packs predominantly have a GPK mystery.
(my blisters were strictly this division, but there may be some variation)
if you're able to just snag yellow header packs with Wackys, each blister is 8/45 = 18% commons, and 2/10 = 20% rare.
which makes them even steven, if you're able to pick and choose your blisters.