While I don’t think that one-shot blink effects like Cloudshift offer enough value to earn a slot, repeatable blink effects that offer ongoing value certainly do. Conjurer’s Closet, in this case, is just a placeholder card: you can (and should) play Thassa, Deep-Dwelling, Teleportation Circle, Nahiri’s Resolve and of course Soulherder in addition to the Closet. These cards allow you to continue to get consistent value from the creatures you’ve already played, and highlight the importance of cheap cantrip creatures: if all else fails, just blink a Wall of Omens and draw an extra card.