It doesn't seem we will agree regarding steep descents, though. People generally have their hiking poles adjusted to a comfortable length for their height and nobody wants to stop and re-adjust them on the go when the terrain is variable.
For me, if the landing spot is 6 or 8 or even 10 inches below my feet that means that it's near inevitable that I need to bend forward to plant the poles so my preference is to squat slightly and use my hands to to steady myself to the sides.
If people are doing that then they are using the poles incorrectly.
If you do not adjust for uphill, flat and downhill then they will be the wrong length .
To be comfortable for your height the poles must be adjusted for each. Uphill they need to be shorter and downhill longer. Mine have quick release clamps and have numbers each cm so I know where to move them too, and so it is easy and only a few seconds per pole to adjust them.
With your poles too short I can see why you are stooping forward, but that is precisely why they should be longer. Longer poles means that you just reach down plant the poles and then step down. A straight spine is also going to mean that your back muscles will be worked less hard. Stooping forward with a 20kg backpack will also be quite dangerous.
It has to be exceptionally steep before I stop using my poles. For the heights you mention, poles would still be used. The greater step height would see me with two poles firmly planted and so when my body is being lowered it is being done so on two poles (arms) and one knee, rather than only one knee. My knees thank me for this. My back also thanks me for this (I did my back in my late twenties and managing it well sees it only have the occasional flare-up).
Squatting a lot would increase the coughulative strain on my knees. I am managing my knees as I want to keep walking for decades yet. The damage is only slight at present, but the wear and tear is coughulative and so by reducing the wear and tear on them now I am increasing my future quality of life.
Generally I much prefer to have my hands free rather than have them holding poles - much of the time when walking/trekking I have my DSLR in hand ready for whatever wildlife shots (or candid shots of Mrs V) might present themselves at short notice (the lens makes it awkward to have the camera bouncing around my neck).
I do understand your point and preference here. However I personally will go with improved safety and comfort during the walk. I also now use my mobile phone (image quality has vastly improved) alone for many hikes. Rare are the days now, when like my first trip to Nepal where I lugged around 2kg of camera and lenses, that I will even take my DLSR (It was film back then).
FWIW, at age 65 I did manage the Path of the Gods last year virtually unscathed, sans poles, although I did save my knees by not doing the 1700-odd steps up from Positano.
We finished the
Path of the Gods walk with the steps straight down to Positano (our BnB was located almost directly below as we were about a 10/15 minute walk out of Positano). From memory it was about an hour of constant steps.
If I had of not done the stairs at the end then yes my knees too would have been much better as that was the section where we repeatedly strained our knees.
Much of the rest of the walk was relatively flattish where you swing the leg rather than step up or down continually, as you are essentially going along the coast on a path that goes up and down a bit, but not that much compared to the steps. And after having also walked down the many steps the day prior from the top of Capri to the port the two longish steep descents on consecutive days sans poles left me with sore knees. I have walked with poles both before and after that for longer descents (and ascents), and with a heavier pack, over repeated days and had no problems at all re soreness.
For myself there is no doubt, walking poles do make a huge difference to the state of my knee. Overall my body pulls also up much better and also at the end of the day I will feel less tired. But as with all things in life it is individual choice as to what is the best trade-off for oneself.
I also find walking down steps/ steep terrain strains my knees more than going up.