I agree with your objective observations but my subjective opinions are the exact opposite of yours. I think the 560S has great bass while the 58X has bad bloated bass, and the 560S has exciting treble while the 58X has poor treble and is too dark as a result.

The 58X were some of my first open-back headphones and I liked them at the time, but they haven't really held up against my later purchases and I'm considering selling them. The 560S is still my favourite neutral reference and an excellent all-rounder, if no longer the best headphone I have.

Bottom line, the beauty of headphones is really in the ear of the beholder.