Are you sure about incorrect refilling in the PC channel ?.
My nozzle checks are like this one (except for the cyan problem). Photo Cyan looks as dense as Cyan and it’s been like this since I own the Pro10S. No wrong ink for sure.
Likewise, you can’t tell apart Gray, MBK and PBK. Instead, Magenta does indeed looks darker than Photomagenta.
View attachment 9379
@palombian
The nozzle test that you posted looks good to me, no artifacts at all. Chroma optimizer stripe is obtained applying chroma on top of gray or black ink in two vertical bands alternating with two bands where no chroma is ejected, so the user can see whether CO nozzles are firing correctly or not. The shinny, darker and slightly wrinkled bands are the parts covered with CO.
Anyway, to show correctly a nozzle test it's better to scan the page. Handheld photos are usually skewed or distorted and sometimes unevenly lighted, like this one. where the right side is darker, probably because of the shadows projected by the photographer itself.
Incidentally, the firmware version of your “potential” printer is v1.100 while my unit is v1.000 and the OP machine is v1.030. My Pro10s was purchased in June 2018 so, if firmware versions are something to go by, your printer must be quite new, but only Canon knows for sure.
I wonder what kind of “improvements” they made from v1.000 to v 1.100. No, I’m not interested on updating (if it were possible), If it works, don’t fix it..