I had exactly the same experience - not with the Truthear Zero, but with the new 7hz Zero 2. The Zero 2s have terrific measurement and rave reviews, but to me they sounded simply awful. Just as you describe, thin, glassy, shrill. I returned the first set, convinced they were defective, but the second set were the same.After more than one year with Truthear Zero I can say that the sound they produce is just not my cup of tea. I returned my first pair in exchange for a new one (I thought that something was wrong with my first pair). Nothing changed. The glassy treble is still there, the mids are very thin. I am not sure what it depends on. I have other headphones that in measurements follow the Harman curve. None of them sounds this bad.
The Truthears have a different design, a more protruding nozzle which I'm now convinced is why they sound so much better to me. I think the reason so many of us have very different experiences with iems comes down to simple anatomy.
For me the Truthears sound absolutely gorgeous.
Bob
ps
We may disagree about earbuds apparently we both appreciate Martinu.