I'm kinda surprised nobody noticed this before.
OPT doesn't guarantee victory. Look at the Tic-Tac-Toe equivalent. The worst-case is a tie, when is what you get when the second player takes their best move. We already know what OPT is for StarCraft: a turtling douchebag.
It's actually trying to win that gets you killed.
Oh well. Nevermind.