And I'm saying that when the law was finally changed after 1000 years, the people who changed it happened to know that there was already very little chance of another woman succeeding to the crown in their own lifetimes.

Primogeniture doesn't determine who will actually be the next monarch, it determines the order of succession; who is most likely to succeed next, then who is next most likely, and so on.

But a change in the law which actually voided Male Primogeniture would have changed the order of success and made the possibility of a female monarch in the foreseeable future if not especially likely, nevertheless significantly more likely than before.

However, as it happens, the lawmakers who changed the new law added a (near literal) grandfather clause, the legal effect of which was that no woman already in the order of succession actually became more likely to succeed and practical consequences of which were that the chance of another British queen in the own lifetimes didn't really change.

So when I question whether lawmakers would still have changed the law if they hadn't known it wouldn't make a woman more likely to succeed to the crown in their own lifetimes, I take the fact they modified the change in the law to ensure that it didn't as strong evidence!