Nobody lasts 17h in constant use, so what is your point (no phones, no tablets). The 6 and 6+ are at the top for battery range when compared to other phones doing similar tasks.
In light use, a phone can easily last a day, and sometimes even two. If you use it only as a phone, with a light amount of calling (no smart functions), a new iphone will many days. So, if it did what feature phones did, it would last 3-4 days.
The use you make of it is what differentiate how long the battery lasts, not just the size of the battery. Apple and all others tries to make a device that will fit say 90% of people's use. The 10% that need full power for 17h, well they can charge their phone or carry a battery pack.
I can kill my phone in 4h if I play the most intense, graphically complex FPS on the phone. So, should I bitch because I can't have it do that 17h? That would make no sense.