That makes no sense. The US Galaxy S7 has the same SoC. They directly compete in terms of performance.
That is what the 5X is- a better phone on paper than the Nexus 5 (in some ways by far) for near the same price (or way less for us over here in the States). From what I understand your main complaint it is has an 808, even though an 808 is better than (especially on the GPU) the Nexus 5's 800. Even if the SoC isn't all better, upgrades like the much better camera or fingerprint reader makes the 5X "noticeably better."
Ignoring the 5X for a second, the Galaxy S6 also hits every single mark for you (if you can find it discounted, I don't know European prices so I have to assume based on what I see). The Galaxy S6 is:
1. Faster - its SoC slays the 800 and it has way faster storage which is actually a bigger deal.
2. Has a way better camera
3. Has a decent battery life with a 6.0 ROM on it
4. Fingerprint sensor
5. Has the exact size of screen you want
The Galaxy S6 hits every requirement (if the price isn't crazy in Europe) easily, but obviously you are Nexus-focused so there must be "oh and no Touchwiz bloat" requirement you aren't stating.
Given that, what you are really complaining about OP isn't that value hasn't moved forward since the Nexus 5 but instead that:
1. Phones overall are bigger and people prefer bigger phones leaving fewer options for true 5 inch phones
2. Google's flagship is the big model not the 5 inch model
3. Smartphone SoCs have somewhat stagnated and we aren't getting six month refreshes anymore
4. The 5X kinda sucks not on paper
And I can't argue with any of that. No one can. But that isn't the same thing as "I can't do better than my Nexus 5 for the price."
I am starting to get the feeling that it is me that doesn't know how to use a forum.
I have stated exactly the issue and the reason for a rant in my 1st post.
I don't think I should repeat "everything" in every reply, no? Or am I mistaken? I am honestly asking: I don't mean to be offensive ()
Now, the Nexus 5X is noticeably better, but in Europe costs nearly as much as a Galaxy S7 (479eur vs 560eur). I know, it is not your fault, but still, in Europe, the Nexus 5X is by no means comparable in terms of pricing to the N5.
Also, the Nexus 5X comes only with 32GB and it is not expandable. 3 years ago, and with an 8Mpix camera, 32GB might have been sufficient. Fast forward to today, add 12Mpix camera, and 32GB don't cut it.
The S6 also does not have microSD, but at least it comes in 64GB (515eur).
At that price, I prefer an S7 (569eur), and I'll add an SD card.
I am going to wait to see the (possible) HTC Nexus: if it is not what I am looking for, I'll go for the S7.
I am not focused on Nexus (although I do prefer it), but Google has gone crazy, in my opinion, with the 5X (underwhelming) and the 6P (too large).
And I agree with your overview: phones have gotten bigger, CPU have stagnated for 3 years.
Which were exactly my points: despite, literally, thousands of phones, there are no mid-range (read, 400eur) phones which are noticeably better than a 3 year old Nexus 5.
EDIT: conversely, there are gazillions of decent phones at 5.5" at very low prices.
After all, basically, the leading phones today are Galaxy S6/S7 (5.1") and the iPhone (4.7", but with "huge" frame): one would think that other companies would try to get a piece of the pie with midrange phones in those sizes. Apparently, not.