The 'balance' is entirely irrelevant, the neutral may end up carrying 20 amps but it is still not
a '"current carrying conductor" in regards to derating.
As far as the non-linear load issue that is up to the installer and inspector to determine.
As I said IMO
the described receptacles "9ea. 20A recep. circuits in clinical exam rooms." Do not sound to me like the major potion of the load will be non-linear.
Your always free to count the neutral as a CCC if you want to, generally I do not.