Jerry once said that any phone that's more expensive than a 2015 Moto G is overpriced.
I know that's a joke, but it's a pretty good jab at how the $600+ phones aren't necessarily $200+ better than one of the sub-$400 phones we got last year.
Even a phone around $200 like the Moto G delivers a solid experience without breaking the bank. You get better stuff on a flagship, but something like the G delivers on the basics fairly well, and for some, that's all they need.
Personally, I don't mind spending big bucks on a phone. I keep mine for 2 years or more, so I want the absolute best I can get at that time period.
I'm not going to drop that far on the reasonable price number, but Jerry's point and yours are valid. I'd just out the cap at within $50 of the current Nexus flagship, because that's the device against which the tradeoffs in whatever features and price will exist most starkly.
(Obviously the below is IMO)
HTC pros over Nexus 6P:
Smaller (if you like that)
Audio DAC
Visual design (back of device)
Newness
Camera, probably
Can be purchased from some carriers
Slight nod to processor
Nexus Pros over HTC:
Screen quality
Battery life, probably
Visual design (front of device)
Front facing speakers
Fingerprint scanner quality
Software quality
Software update speed
Security and security updates
Price
Storage options
Carrier usability
Can't call it yet:
Build quality
Build materials
Fingerprint scanner location
So looking at those lists, you can't just say which has a bigger list - you have to find the features most important to you and then decide, once you figure out where most of your desired things are, if the different things are improved enough to make the price difference equate to a good value.
For me, they're so close on do much and the things that I care most about are in the Nexus column, that even though I think the HTC is the best non Nexus so far this year, I couldn't justify paying $200+ more on it when I'd consider the Nexus a "better" phone for me. If the feature balance went the other way then it'd be a little more difficult, but IMO the HTC should be $499 base and on sale for $449 with promotion to be a winning VALUE.
That said, $699 base is probably where their acceptable margin less promotion and not sold stock exists. So going lower to lose money on sales would be a mistake. They're not fighting for share this year, they're fighting for reputation and to reestablish relevance.