I tend to agree. I had the famous honeymoon when I first started hCG at 2000 IU a week. lasted the typical 2 weeks, never to come back again.
Just like you, I think the initial hCG dose cause some changes in hormones and neurotransmitters which reached the golden ratio, ergo libido, wellbeing, etc. As soon as the body starting fighting back to achieve homeostasis, the feeling was gone. In retrospect, I should have run to Quest the moment I felt like 20 years old and have my markers checked. Not a guarantee for success, but at least I'd have a better reference.
My hypothesis is that it's not that levels (of anything) have fallen, or risen, that causes most of the reasons people are in this forum, but that for some unknown reason, the body has changed the set point, and it's regulating it to a level that is not what we want, so in essence, doesn't really matter much what we do, the body will fight back and will try to maintain the new balance it decided to keep. And who knows, maybe there's a reason for it, and maybe it is, ironically, a good reason.
I never subscribed to the theory that it's the change, the flux, that causes the desired effect or that the body "wants variation throughout the day", I think it's just the other way around, there's variation because the body is trying to keep homeostasis and things are changing. Just like the A/C. It doesn't "want to work more during summer" it just detects that it's hotter and has to work more.