Boros Moxite plays a wide board of small creatures like Thraben Inspector, Glint Hawk, and Sneaky Snacker, making Breath Weapon's 2 damage to each non-Dragon creature a strong sweeper against their low-toughness threats. Their removal suite (Journey to Nowhere, Galvanic Blast, Lightning Bolt) can pick off our creatures, so resetting their board with a sweeper buys crucial time. Cut Malevolent Rumble for the swap since it doesn't interact with their board state. Keep ramping toward Tron and use Breath Weapon proactively once several of their creatures are in play.