Esper Control is full of hard counters (Force of Negation, Spell Snare), taxing effects (Narset, Teferi, Time Raveler), and sweepers (Supreme Verdict, Wrath of the Skies), making Summoner's Pact's delayed payment a liability since Narset can strand it and discard effects or counters can leave us unable to pay. Stock Up gives us card selection and refuel potential against their grindy disruption, letting us find our next land drop or threat after a Verdict. Six is a resilient threat that survives sweepers targeting nonland permanents less efficiently and provides card advantage through its attack trigger and retrace. We keep our full land base intact since this is a long game where Amulet of Vigor value and extra land drops via Primeval Titan are how we out-grind their card advantage engines.