HOGWASH! Doesn't matter who the opposite party is. You bet one way, somebody else bets the opposite. At the time of the trade, both are convinced they are correct for doing so.... otherwise, they wouldn't take the trade.
But you still don't know how the winning rate of your opponent is. So your statement that you would never trade against a 90% winner cannot be checked, and that was your point. Your statement is wrong.
You trade because you THINK the odds are in your favor...., but in reality it can be completely different. Reality counts, not what you think. Because if what you think would count you would win every time. And that is not the case.