Mono-Red Prowess plays bigger threats like Sunspine Lynx (5/4) and Screaming Nemesis (3/3) that dodge Burst Lightning's unkicked 2 damage, so Scorching Shot's 5 damage is a much better answer to them. Spell Pierce is a cheap way to protect your own prowess creatures from noncreature removal like Reckless Rage or Burst Lightning on key turns, and it can also counter their noncreature spells such as Kumano Faces Kakkazan or Monstrous Rage early in a fast race. It can't counter their creature spells, so it won't stop Sunspine Lynx. Boomerang Basics is weak here since they have few high-value permanents worth bouncing and every card matters in a fast race. Screaming Nemesis is excellent in this matchup since it punishes their damage-based removal like Burst Lightning and Reckless Rage.