I finally got a new iPhone for the first time in six years and the difference is staggering. Things are advancing so fast that there’s really no reason to go cradle to grave anymore.
6ys is definitely a long time for a phone. Personally, I'm trying for 5yrs on my 13 Pro. It'll be 3yrs in February.
For each iPhone I've had, I've extended the time between upgrades by a year. 4S to 6+ was about 2yrs. Then to the X was 3yrs. And then 4yrs til my 13 Pro. The cost is one of bigger reasons driving me to do this, but I take the opposite opinion: the advances model to model aren't that major to me. I don't need a more powerful/capable camera or a screen with a deeper black or whatever. Aside from calls, messaging, emails, and reading news, and the occasional photo/video -- usually of nothing of great importance -- nothing I do really pushes my phone to its limits.
That said, I'm somewhat considering doing an earlier upgrade because of that satellite connectivity feature. Not that I go off-grid or anywhere with poor reception with any regularity, but I feel like that's a nice safety feature in case of an emergency.