Look, I actually didn't realize that in the Medieval era belief in witches was less common, but I have never seen anyone claim it is in the Bible that witches were once real but were no longer real. That is where I think your hypothesis breaks down.
You are doing exactly what a rational person would do: you don't believe witches exist today (thanks in no small part due to advances in knowledge, so it no longer requires theological guessing games), but I think the way you arrived at that perfectly rational conclusion is not necessarily reflected in the Bible, hence the ability of people in the 17th century to think that it WAS a matter of faith.
Here's where I think your position feels more like haughty pride rather than reasoning and teaching:
You act like it is somehow SELF EVIDENT that the open-ended and completely witch-agnostic verse from Acts is somehow a clear indication that Witches no longer exist. It doesn't say that AT ALL. You could have grabbed any open-ended comment and said "See, that means God made witches non-existent after this date!" And you denigrate those who fail to have the same amount of imagination as YOU DO.
Secondly you act as if your sects' particular penchant for Dispensation Theology (not common across all Christian sects) is the be-all and end-all of theology. VERY chauvanistic of you. You are sitting in judgement of other Christians.
Thirdly you act as if you are somehow spreading all this great knowledge but everyone who fails to read the Bible with your special seeing-stones (or whatever you use) is somehow "less educated" than you are.
The self-reflective man might actually say to himself: "This is my belief and this is how I justify it, but I can certainly see how YOU might not see it that way because it is not obvious and is shared by few if anyone else."