I totally agree. My first smartphone and iPhone was the 4s. Then I hung on to that for 4 years (though the last year was rough) and then got the SE. That was a massive jump:
-better camera
-bigger screen (but still fits great in my hand and pocket)
-more RAM
-Touch ID
-faster CPU and more responsive
-motion processor
-ability to do Apple Pay (which I don't use)
I've had it for three years now and I just got a new battery put in the SE. iOS 12 works fine on it, so I can see myself using this for at least another year, if not two.
I really don't get the yearly or even every two year upgrade cycle. Is the improvement really enough to justify the expense of the Apple tax that we pay, especially for those of us regular consumers who don't really do professional level work which require top-level performance?
I've gone through the same thing with the iPad. My first one is the iPad Air that I got in early 2014 and it still works. Recently when the new iPad Air (10.5 inches) was released, I got the iPad Pro 10.5in from 2017 (256GB), as several people online recommended. It works great so far and I can see myself using this for another 4-5 years easy if I don't damage it. It's also a fairly big improvement from the original Air in several ways, so it's worth the money for me.
I'm still using my first MacBook Pro, non-retina from 2012, upgraded to 250GB SSD and 8GB RAM. I finally upgraded from Sierra 10.12.6 to Mojave 10.14.4 about 10 days ago, skipping over the High Sierra issues altogether. Overall it's been going for nearly 7 full years now, and besides the two dead hard drive cables and the time the RAM chips somehow popped loose, it's been pretty good. I'm holding onto this as long as it works and does what I need it to do.
When it finally comes time to replace it, if Apple hasn't fixed the butterfly keyboard problem plaguing the new MBP since 2016, then I'll look into getting a 2015 MBP. I can't wait weeks for my keyboard to get fixed.