Once Sephiroth flips, which is easy to achieve with an Accursed Marauder or any kind of Grave Pact effect, the Blood Artist effect becomes permanent, and you get access to a terrifying 5/5 Flier that can draw you several cards a turn
That alone makes them extremely powerful - starting a game with extra card in hand, and one that is guaranteed to work well with your strategy, gives an tremendous advantage over players who don't use one, and most of their deckbuilding restrictions were either easy to fulfill, or had enough loopholes to work around them
Best White Ramp Payoffs There are different ways to abuse these white ramp spells, especially the ones that have a creature attached
In any case, these one-use flicker cards almost never do anything else to impact the game, so increasing their density to have access to them all the time is filling your deck up with situationally-useless cards