My personal experience feels as though it matches your predicted 70% win rate. It feels like I almost always win.
Anecdotally, I've won a few times with AAB by spinning an A that has 3 available spins rather than "wasting" B's final spin. Of course, that's hardly conclusive since we're talking about randomness here. Any wrong strategy can potentially work... sometimes. If you're sure that spinning B is ALWAYS the right option, I can update my tactics.
Of course in silver/bronze you don't want to win a card you already have 6 of, but in Gold/Plat, winning SOMETHING is worth a minimum of 1000 electrum, therefore the True Optimal Path matters.