Boros Dwarves is an aggressive go-wide equipment deck (Dwarven Mauler, Iron Hills Blacksmith, Leyline Axe), making Slagstorm's 3 damage sweeper very effective at resetting their board before equipment snowballs out of control. Sear kills their bigger equipped threats or Thorin, Mountain-king at instant speed, which Shock and Burst Lightning often can't handle once boots or axes are attached. Sunspine Lynx is weaker here since they run mostly basics and shocklands, limiting the damage payoff, and Channeled Dragonfire's 2 damage is frequently insufficient against buffed creatures. This matchup is a race, so use the sweeper primarily when behind on board.