They are not really wrong, in essence. They would work fine for a bump. But parallax occlusion uses the alpha for the height. The lowest could be either transparent or white (or black and then inverted). Your normal does not have these differences to make a proper height.
Check out these two example textures and compare them to your version:
You’ll see what I mean.
Edit: my apologies, the lowest needs to be transparent I believe. Not sure though. May be it converts it to alpha but then may be not. Best is to have it transparent; understand use the alpha for the height.