They were banned for 40 years until 1992. There was at least one woman playing AA ball prior to that ban. It’s possible a woman might have advanced to AAA or even the big leagues had they been given a chance. It’s true that they are on average less physically capable than men. But there are physically exceptional women. I could see a female pitcher possibly doing well by virtue of the fact that the men are not used to her style of delivery. For the same reason knuckleballers sometimes do well even though they throw slowly.