First...my comments aren't directed specifically at you but others' comments/expectations commonly found in Nexus threads.
We go through this exercise every year. Rumors of the upcoming Nexus start to surface, foillowed by the endless, 'if they just improve XYZ feature' or 'add ABC to the phone', it'll be the perfect Android phone. And every year, people express surprise or dismay at the capabilities, design, etc of the actual phone. This will be the 9th Nexus phone---why on Earth do people think Google is all of a sudden going to change their routine?
There have been hundreds of Android phones yet I've still yet to see the one phone that will seriously tempt me to jump ship full time to Android--top of the line, industry leading hardware that's unlocked/carrier free running stock Android with timely updates. If they could've waited until this generation of hardware to try the GPE experiment, I'd jump all over a Samsung S7 GPE.
I have faint hope that the rumored 'Google phone' will come to fruition and that they are positioning it as a flagship level device slotted above the Nexus phones and comes with comparative hardware. Not holding my breath though.
I hear ya, but it's also true to say each Nexus device has become better, more marketable, more accessible to mainstream, etc. than the last. No?
The Nexus 6P, I think, finally crossed that line into a seriously viable Android flagship candidate. Good price point, top-line specs for its time, finally a great camera, reliable fingerprint scanner, solid build, and a unique design (if a little polarizing). And the often praised clean Android experience and direct Google updates. Everything was at the very least 'good,' and there were no obvious nor major deal-breakers (maybe the size?). Can't say the same about the 5X unfortunately, but the 6P really did the job.
I don't think it's unreasonable to hope that Google will deliver another great Nexus option this year, too. Unfortunately, the leaked specs and designs so far seem rather uninspiring.
I think the process you describe applies to nearly every rumor of every future device. A mix bag of cautious optimism, complaining, wishful thinking, etc. Perhaps it happens more with Nexus devices because everyone sees the Nexus line as some saving grace in the Android space; the "one" so to speak that's supposed to bring balance to the Force -- er, I mean, to Android. So perhaps expectations are raised a little, too.