I think the ideal is to set the bars even or slightly higher, either with a threaded stem at max height or a thread less with spacers, then gradually lower it, until you find the sweet spot, this is going to be different for different riders, and may even be different from one bike to another for the same rider. There is no hard and fast rule that bar height must have a certain amount of drop.

Where it gets interesting is that some riders, have the idea that you need this massive amount of drop, and in order to get enough drop, they go with a too small frame, put the bars as low as possible and jack the saddle way up. I think this is one of the reasons that back in the day they would recommend a 58cm frame and today they recommend a 56 or even a 54cm frame for the same rider. The recommendation in the 1970's was to put a leg over the top tube, if there was a couple of inches of clearance, you were good. They would give about 3 inches (a fist full) of seat post. Generally considering that the seatpost clamp and headset locknut were about the same height, there would be 2-4 inches of stem showing. This meant the bars were somewhere between 1" above and 2" below, depending on the height of the saddle and the stem.