I observed that different kinds of labor require skills that differ qualitatively, yet by the inherent attributes of labor emerges no particular ranking among the kinds.
You are conflating a duration of time invested acquiring a particular skill, which is quantitative, and therefore may be ranked, if desired, with a skill itself.
Are you asserting that skills otherwuse differing only qualitatively are related by a ranking, based on the duration of time invested in acquiring them?
Are you using word salad to deny workers their lifelong earned skill sets by assigning an esoteric value judgment based on the level to which YOU deem it necessary for justice?
You deny someone their skill when you say they can't have more or less of it. If skill can be obtained and improved, then it can be more so or less so.