As someone who flagged this issue, I'll give my perspective here.
For one thing, it seems really strange to me that you mention that Cort Ammon, Bill Watts, and Dale's answers being invalidated, yet you don't mention my answer. My answer was posted a day before the other answers, and was afterwards invalidated by an edit from OP. Dale's answer also had this happen, and Dale even made a comment; but he chose to edit his answer instead to address the (substantially changed) question.
I don't think that's fair. OP originally asked a question, and I spent time answering it. Then, they decided to just change the question and add an example that seemed to feature completely wrong math (I was talking about this in the conversation moved to chat).
Why should the later answers be made relevant when I had been the first one to come to the problem and spend time answering it in its original form?
There's no completely fair approach here; but to me it makes perfect sense to keep the original version of the question which was answered. Why should the person who was first to help have their answer made nearly irrelevant? If anything, this shows that changing a question after it was asked is unfair, because if people answered before and after the edits, someone is getting the short end of the stick either way, and it's not really the fault of the one answering, since checking the history of a question to make sure it didn't change too much shouldn't be necessary before writing an answer.
As far as the close votes go, there's only 2 now. I had actually cast a close vote after the edits from OP, because most of what they added was math that basically didn't show anything relevant, and made the question very confusing. Since the question was changed back to its original form (which I didn't think was unclear enough to close, which is why I answered it), I just retracted my close vote.