Temporal Cleansing

The reach is the story. Blue rarely gets a clean answer to a permanent it cannot bounce, counter, or race, and this touches anything nonland: an indestructible attacker, a resolved planeswalker, an enchantment lock, an artifact engine the color otherwise has to route around. What it does not do is exile, and that gap is deliberate, because the choice belongs to the target's owner, not the caster. Tucking to the bottom is genuine removal against most decks (the permanent is a shuffle away from ever mattering again), but the second-from-top option is a mercy the owner takes when they would rather draw the thing back in two turns than lose it for the game. You are not choosing between removal and tempo; you are offering the opponent the least-bad version of losing their permanent, and against a deck that wants its threat back sooner, this can whiff into a two-turn delay. Convoke is what pays for even that much reach. A flexible four-mana blue answer to any nonland permanent would sit outside tempo range if you had to pay it in lands, so the design lets a committed board tap in to cast it early, converting bodies you were not attacking with into the mana that clears the way. That subsidy is the balancing lever: the spell wants a caster who has already built a board, which keeps it away from the lean control shells that would most want it cheap.