True. There's a reason why the 6s is still supported. The general hardware performance have caught up to provide good enough user experience. The rest are just icing and cherry on the cake (better camera quality, better screen, better battery life, etc).The older you get, the longer you wait to upgrade. I have the 12Pro in gold to match my AW5 SS Gold, so I am in no hurry to change either one. We getting to the point of diminishing returns. At my age, I don't think there will be a significant improvements for a couple more years, Quite happy with what I have.
When I use my 7+, I don't feel like I need a faster phone. The only thing that feels old about it, other than its design, is its camera quality (it is obvious, even my Galaxy A71 can deliver better looking photos). But the rest, it doesn't feel lacking at all.
OTOH, for some people, a phone has become fashion accessory, thus the need to change on a yearly (or more frequent) basis. It's just the nature of the maturity of the tech.