I don't think it really matters what Android device comes out. Most of these iPhone users don't care. They are used to what they have, their friends have iPhones and the have no reason or desire to change.
I can't tell you how many people I've dealt with who allowed a salesperson to talk them into the latest Android device and within days they want to go back.
"It's too different" "I can't see when my friends are responding to my text" (ala iMessage) "My Apps look different" and on it goes. Most of these iPhone users just want a shiny new iPhone and if they can afford it they will buy it.
I personally have one of each and the iPhone is my primary. My entire family is on iPhones and the times I stepped away to try out the latest HTC or Motorola (I personally do not like Samsung phones - I do like their TVs) device it was annoying and I aways came back.
You're right, Apple's influence over its customers has successfully created terrific brand loyalty. I've been enjoying Apple products since 1991.
However Apple's brand loyalty seems to be fading. As you mentioned "I can't tell you how many people I've dealt with who allowed a salesperson to talk them into the latest Android device." If they were completely happy, no sales person could influence them.
I have enjoyed every iPhone since the first. Working in a multi-platform environment for years, I do like to use computers and smartphones of all types concurrently. It provides the variety and first hand experience required to stay well educated and up to date.
My Nexus 6P is my favorite and primary smartphone of choice. Faster, smoother and offering greater functionality, Google's to be congratulated for surging to the front of the pack.
That said, my iPhone 6S Plus does do well as a secondary phone. Had Apple not stopped progressing, and had they not allowed quality and the user experience to deteriorate, my iPhone would still be my favorite and primary smartphone.