You make good points - hard to argue against them.

The AD and the ADP are IMO not bad at all when one gets a proper fit. I could say the same thing about Lambdas. IMO it is easier to get proper fit with the Paradox thought. I think both the Paradox and the ADs are tuned towards similar tone goals.

I agree with you that EL-8C, LCD-XC, TH900, and Sony Z7 are proly not up to snuff.

The Focal Spirit Pro are not too bad, but they were a bit uncomfortable for me.

Some lossless, some lossy.  Didn't matter either way though.  I don't think that's a good comparison either since harmonic distortion doesn't really sound like encoding artifacts.

Maybe that one was just particularly good or something.  I couldn't really comment since I've only heard one.

My plan for my next closed headphone is is to turn a SR-207 I picked up cheap into a DIY 4070.  If that doesn't work out I may check into the Paradox.

The psychoacoustics of this would seem to get very complicated.

IME things with high-ish D2 in the midrange give female vocals a lush and syrupy quality that I enjoy.  I think that's why D2 is sometimes considered euphonic, or at least less offensive.

Unfortunately harmonic distortion always comes with intermodulation distortion so those lush vocals also come with a reduction in separation and imaging.  If the high-ish D2 continues up into the treble then all the separation goes to hell in a busy passage and it just turns in to a wall of sound.

What one likes and what ones will put up with may also vary depending on ones particular sensitivities.  If someone just just listens to "audiophile" recordings female vocals with light accompaniment, small jazz ensembles, or something like that then they might not mind higher levels of D2.

OTOH, my primary genre is metal. The guitar's come with just the right amount of distortion pre-added.  They don't need any more, thank you very much.  The imaging will go to hell if you do.  The Alpha Dogs I heard had the T50RPs usual lush mids but the imaging in busy passages didn't go to hell.  It actually kept it together pretty well.  From that I'd assume that the distortion on that pair wasn't particularly high and that it confined itself to the mids.

Beyond that, you and I just may be looking for different things in headphones.  I don't remember reading anything where enumerated some kind of broad outline but I gather that in general you're looking for ultimate resolution.  What I'm looking for is a little different.  First and foremost it shouldn't be fatiguing.  I should be able to listen to it for as long as I want to without mental or aural fatigue.  It doesn't matter what else it does right if it makes my ears bleed, literally or metaphorically.  Second would be separation.  I like to hear every individual instrument, each individual reverb, and every single guitar overdub.

If there was a perfect headphone then my goals would probably be subsumed by yours but since there isn't we all have to make different tradeoffs.