I certainly don't want to, but fact is my brakes now are significantly worse than before the swap, so going back (but with new MC and calipers) would at least give a reset to where I know how it "should" work and feel. ...
"I feel your pain"
Everything you've said resonates with me.
My only remark at this time is: Replacing the system you have with the QTU/LD system is, in effect, replacing a simple system with one that is more complex.
Occam's Razor can be mis-applied here with relevance: The simpler system is more likely to perform as intended.
Afterthought: I haven't retreated through this thread to see if you've replaced your hoses and confirmed you have solid plumbing throughout the system. I remember you've fussed with the ABS. I came away believing you were diligent in your work.
I mentioned this earlier: When I added the SS hoses and larger rear cylinders, the brakes improved notably. I forgot to mention that I also replaced a ruptured rear hardline at the same time. In fact, the hardline ruptured first, and I took the opportunity to install the SS hoses and rear cylinders during the repair, in one work-event.
For all I know, prior to the rupture, the section of rear hardline was soft/thin and, while not yet leaking, swelled under pressure to the detriment of the brakes' performance (this is speculation on my part).
The punchline is that, unless you know everything is in primo condition, you may have a devil lurking in some hiding place.
Keep us informed!