In addition to the ink cost, there's one more thing to remember which is that not every card can be used in the inkwell
Discard spells (such as Thoughtseize, Inquisition of Kozilek), cantrips (such as Serum Visions, Opt), countermagic (such as Mana Leak, Force of Negation, Drown in the Loch) or even removals (such as Fatal Push, Lightning Bolt, Kolaghan's Command, Drown in the Loch) are checking and slamming the battlefield
Everything is available in standard and foil, alongside the Japanese variants as well
A great pick for our Minotaur Tribal build
But for now, they are more fun than truly competitive
Its more that if the card did everything people anticipated it to or claims it currently does, it would instead be more in the range of third best