If Threshold were a mechanic, it would be continuously linked to having seven cards in your graveyard, thus wouldnt require spelling it out on the card
These cards are classy and would make a great full-set collector's item, but given that they're only for rare or mythic rare Heroes and Villains, they're going to be difficult to find in packs without having to buy some as singles
Its a natural fit for aristocrats-style builds, where cards like Grave Pact or Dictate of Erebos keep opponents sacrificing while Venom turns the fallout into both size and value
As a mana doubler that comes with a dork, you get a huge advantage, one magnified when you play a turn-1 Llanowar Elves
This is a real issue when most Vintage Cubes have a Black Lotus, all the Moxen, Time Walk, and more