Besides removing a few features, there's little difference between an iPhone 6 plus and the current model.
Upgraded to XS after wading into a pool with my 6. Biggest hidden feature is the electronic SIM card. I can buy international data with GigSky for much cheaper than AT&T would let me.
I was in Iceland for a week, so 2GB for 15 days and $30 worked well. (I was on the fence about 5GB for 30 days and $50, but in the end didn’t need it.)
This will be a term problem for many phone manufacturers, the market does not grow as fast anymore + people keep their phones for more cycles. Anecdotically, many of my friends and family members would upgrade their iPhones every two years. Now most of them are still using the 6s, SE or even 5s.
My hope is that now other phones have introduced touch sensors under their screens, that Apple will add that back in.
Apple could have been first to support an in-screen fingerprint reader but stopped development when FaceID was greenlit. It's doubtful they would follow others in including a redundant, inferior technology (their perception).
They said 4 inch was the perfect screen size. And now? They shunned wireless charging, dual sim, multi-tasking and many other things.
Give it time. Apple will soon invent in-display finger print.
After using FaceId for over a year, going back to TouchId really does feel like a step backward anytime I have to use it on test devices or my iPad.
What they took away from iphone 6 is interesting however. The home button, headphone jack, earpods, and rectangular display.