Jeskai Artifacts leans on Goblin Welder and Goblin Engineer to cheat artifact creatures like Phyrexian Dragon Engine and Pinnacle Emissary into play from the graveyard, so Containment Priest shuts off those tricks by exiling any nontoken creature that enters without being cast. It does nothing against the Construct tokens from Urza's Saga, since those are tokens. Prismatic Ending is cheap exile removal for their low-cost nonland permanents such as Goblin Welder, Mox Opal, Lotus Petal, the Baubles and Sewer-veillance Cam. Converge limits it to a mana value no higher than the number of colors we spend, so one color hits mana value 1 or less and both W and U reach mana value 2 (Goblin Engineer, Loki). It cannot target lands, so Urza's Saga is off the table, and Emry or anything else with mana value 3 or more is out of reach. That cheap interaction is much more relevant than Daze tempo plays against a deck full of free spells like Lotus Petal and Mox Opal. Snapcaster Mage is a lower priority rebuy piece when we need more proactive hate against their engine, so we trim one copy for interaction.