What they should have done is still offered a phone that works well for one handed use according to Steve's guidelines because fact of the matter is phones are supposed to be pocketable devices that can quickly and easily be accessed with one hand while on the go, doing other tasks, etc.
If Apple wanted to offer a larger phone for the Android phablet loving crowd then so be it but it was a dumb move to offer TWO larger phones. Now consumers are faced with the option of big or bigger, dumb or dumber.
Both devices are awkward to use one handed. If I had this to do all over again and I had to upgrade I would have gone with the 6 plus because if you're going to have to struggle with an awkwardly sized "phone" then you might as well get the full, oversized, large screen, awkward experience.
To you and those that keep bringing up the 5S as an option. The 5S does not offer Apple Pay which will be huge and is a very important/crucial feature for myself and many others that have ever had their credit card data stolen.
And for those people claiming the 6 is the right size for one handed use, you are wrong. I'll provide you with this very nice and detailed mock up Mashable did on one handed use. Take note of the "thumb zone" image.
I will say it again but you are dead wrong with this insistence that the 6 cannot be used one handed. That link is completely bogus. Change the way you hold it ever so slightly and you can reach 95% of the screen easily, and the 5% you can't reach probably accounts for less than 1% of usage. I'm 5'6" with average hands and by shifting my grip up slightly which is not at all uncomfortable thanks to the new design I can reach everything from the home button to the top of the screen. Everything but the very further most upper corner from whichever hand I'm using.
In your case you really are 'holding it wrong.'