Tron has almost no creatures worth Cast Down early (their threats like Bramble Wurm, Maelstrom Colossus, and Pinnacle Kill-Ship come down turn 4+ after ramping), so trimming a copy for proactive disruption is worth it. Duress strips their key noncreature spells like Ancient Stirrings, Cleansing Wildfire, or Expedition Map before they assemble Urza's Tower, Urza's Power Plant, and Urza's Mine, denying them the mana to cast their finishers. Since your clock is fast, use Duress on the turns you don't have a creature to deploy to keep pace with their ramp. Keep the rest of your removal suite intact since Bramble Wurm and the cascade creatures still need answers once they land.