Cost aside, the other big problems with cards like Omniscience is their lack of immediate impact and the fact that they taper off once you run out of cards in hand
1) Dark Ritual None of the above instants would be as powerful as they are without the existence of the best mana acceleration card on this side of Black Lotus
This commander helps assassins do what you want them to do, sneak in for lethal
The +1/+1 counters may seem like some compensation for the tap drawback but it is basically just being given a tissue to wipe away the blood from the beating you just received, more humiliating than useful or comforting
nor would they have dared now, if it hadnt been for the grim-voiced Bard urging them on
You wont be outpacing the turbo list, and you likely wont be outvaluing the midrange list, so your goal is to stop your opponents from doing all that much to begin with