Null Rod is strong here because it shuts off the activated abilities of their artifacts: Mox Opal, Lotus Petal, Mishra's Bauble, Urza's Bauble, Sewer-veillance Cam's sacrifice ability, Legion Extruder, and the artifact lands Great Furnace and Seat of the Synod, which cripples their mana and artifact shell. It does not stop Goblin Welder, Goblin Engineer, Emry, or Urza's Saga, since those are creatures or an Enchantment Land rather than artifacts, which is where Disruptor Flute comes in. Disruptor Flute can name Goblin Welder or Emry, Lurker of the Loch to tax them by three mana and also shut off their activated abilities, since those aren't mana abilities. Naming Urza's Saga can't tax it, because it's a land and never cast, but it does stop the chapter II Construct-making ability while leaving its mana ability alone. Chalice of the Void is cut because their deck is full of cheap zero and one-mana artifacts (Lotus Petal, Mishra's Bauble, Mox Opal) that it also stops us from playing, and it doesn't stop their primary engine pieces reliably. Sire of Seven Deaths is too slow against their proactive artifact value engine.