They are related. In other words, don't overthink the difference, which appears to be what you are doing.
Yes it's exactly what I feared. Thank your your help.
And what I understand of your really interresting metaphore is that transparency and neutralty are realated only if the music production is "good", or I caould say "faithful to reality". Reality may be a subjective thing...
Just another thought/explicitness :
What I understand of neutrality, is that the recording does not necesseraly reproduce the "reality" of instruments. It can be just a flat choice of mixing the instruments so that none are proeminent, except maybe the voice. It can also be something totally different depending of artistic choices in the music production. ... and a lot of effect are put on a lots of recording to "sell" the product more (overuse of autotune as an example). And then the neutrality of a system tends to reproduce these choices, whether they are good or not. Electronic music is not "real" so inevitably on the neutral side too.
Transparency. I would not refer to distorsion. Maybe the relation to reality.
A violin can be sibilant (I know the word is not right here but I just empasize the idea.). A mandolin can be harsh sounding sometimes. The singer could sing too loud or too"behind" the scene. Etc.
And for other things that are alright.. We (almost) never really listen to a band for real in a studio.
As you say Fitzcaraldo215 it's vastly subjective. I would define transparency as an "organic" thing. As if could even smell the wood of the instruments.
Uhm...maybe it's listening to a music that is not recorded, but as heard in real time.
In my video comparing the Oppo PM3 and the Grado SR80e, I say that the Oppo is on the neutrality side and the Grado on the transparency side. The response curve of the Grado is ugly, but still, to my hears it sound really good.
Neutrality would be represented by the B&K 1974 optimum Hi-Fi curve.
Transparency maybe by the Harman target response.
Am I wrong ?