Just understand that certain users (especially kids like my son) don't need future-proofing in a smartphone.

That it works and fulfills his needs is all that matters.

I can afford to splurge on a Samsung Galaxy S7 Edge for him, but what is the point?

He is not interested whether it is running the latest Nougat 7.1 or Lollipop 5.1.

But it matters that it runs PokemonGo smoothly for him.

It can easily last him a day. No problem at all.

Hehe nostalgic.

If only it has the bloody back and multitasking buttons, it's still a good backup phone. 

Yup.
But why can't they just follow Google's guideline? How can a swipe be any faster or easier than a click?
Similar to the back button.