Sure, I can buy a new $150 Motorola every year or two, and it would be a good phone, but I could also just buy my top-of-the-line iPhone and keep it a little longer, and it means that I get a really exemplary phone every once in a while.
that would be awesome if true. however when the iphone 6 came out, there was a phone by moto, samsung, and LG that all had the iphone spanked when it comes to specs.
So in practice, if you bought an iphone 6 at launch, you will still be using it in 4 years as you say. in that time you already bought a phone not as good as others already on the market, which are getting upgraded versions over the next few months. which one might buy, use for 2 years.
at this point you are still on a 2 year old iphone 6, which we already established was not the best phone on the market the day of launch, while I am trading in my note 5 to the new shiney, and you are using your iphone 6 for another 2 years.
yes, i went though more phones than you, but i didnt really pay any more to do so.