The combination covers the full picture: reliable baseline data from the APIs, and current market reality from the scraped sources
One of the core principles I use in calculating these drop rates is the ratio of cards in a Draft booster: 10 commons, 3 uncommons, 1 rare or .5 of a mythic rare
And its a fairly affordable promo, sitting at only about $50 compared to the under $20 price tag the New Phyrexia version has
And then mono-black control can lean on it with all their Caged Sun effects and such making your big mana plays like Exsanguinate that also force their foes to sacrifice each turn to Sheoldred, Whispering One
Any commander who has an effect that scales with damage is going to reach for this, to be sure
I imagine the best way to use this is to identify someone else at the table who would really want a new hand, see how much mana they can assist you with, and then leave only enough mana to cast Game Plan with assistance