"If you Google Marcus Hilton basic Foxtrot. The question by the late Harry Smith- Hampshire which was where is the moving foot at the time that the heel of the standing foot lowers to the floor on the third step. It can be clearly seen as being down. But take a look at the lady at the same time on the same step. you will see she hasn't lowered yet. She will not lower untill the moving foot arrives under the body."
If you look carefully, you will see that in actual fact many ladies, and Karen Hilton is a good example, usually have their heel flat on the floor well BEFORE their moving foot gets anywhere near it to end the third step of a feather.
They do this because this is what is required by the large dynamic motion they've chosen to create in these situations. It would be awkward to start seriously absorbing the fall in the knee bend as has now been the norm for many years, while still holding the heel up as you propose.
If you are only watching youtube though, you might not see this as the few pixels representing the heel of the lady's shoe often get lost in the video compression. You may be seeing the heel cup above the floor, and unable to see that the heel tip is actually on it.
And that's not to say that everyone does it all the time. I've seen some video of Alessia for example, where the path of descent is such that she can keep her heel up longer.
The only correct answer to Smith-Hampshire's question is that the proper sequence of events depends on the desired character, not of a step in general, but of the interpretation being executed by a given couple in a given instant. As there have been many interpretations, so there have been many slight variations of the details, each perfectly correct for the situation in which they are used and entirely incorrect for some other situation.