You've made this claim a few times in this thread now. Can you please elaborate as to what about Duplex, specifically, has not worked for you?
Edit: A quick browse through OP's comment history suggests that s/he might not be US-based. Should that be the case, then it's not that Duplex is flawed, it's that it's simply not available where they live.
I have been using the call screening feature on my Original Pixel for months now. It works very well. I can't comment on making reservations via phone, since we don't often go to places that require reservations, but the call screening is great.
Prove that it does work. Because it just doesn't exist at all.
You pointed to an Android fanboy's site.
It's not the reality:
https://mashable.com/article/google-io-2018-report-card-dupl...
This is to put it lightly....