Sorry. If that's so, this should have been more clear.
Light Screen: The Pokemon summons either a golden box to protect itself or golden erect walls to protect it and its teammates. The walls reduce the power of special attacks by 5. The effect lasts for six (6) actions after use.
Attack Power: -- | Accuracy: -- | Energy Cost: 8 | Effect Chance: -- | Typing: Psychic
It says power, not Base Attack Power (usually the descriptions will say exactly "Base Attack Power" with caps, for example at Bulldoze). I have no idea if that's intended or not, but with that said, I have been doing -5 at the end of moves all my time throughout ASB.
If that's so, then it's pretty dumb. It'll definitely be an 8 though.
Heat Wave > 5 + 3 + (4-1 x 1.5) x .67 - 5 = [8.375 Damage/6 Energy]
How about we call it a tie then. Being confused is never fun. Flare will get a KO Counter alongside Bahamut.