Relative ranks might work, but there need to be absolutes for determining quality of a work.
Why not have those be relative too? If ranks could be relative why not the quality of work?
Btw doesn't this seem like it should come with the rewrite of the dorf brain? Relativity seems so far beyond the current dorf thoughts of, "my spouse died, ooo this dining room is amazing!
Quality ranks have a very real place in the code. How much an +iron short sword+ is worth might vary, but it will do as well as any +iron short sword+, even if one was made by a race of masterful dwarven smiths and the other by goblin slaves.