While I agree, we are at the point where any essential services can be done by even phones 7 years old. For example, in the last 7 years, what phone didn't have texting capability? Some would say something like VoLTE is essential, but I'd argue it's a convenience more than anything (that of course will change once carriers drop their 1x and 3G networks). You can still make calls without VoLTE, they may not be as clear but you can still communicate. Maybe fingerprint scanner, but like VoLTE that's more of a convenience than essential. Most all of the features released in the last 3-4 years aren't essential, but a convenience. Even RSC is a convenience.
What I was referring to wasn't a hardline like having or not having texting capability, but seeing a perceptible difference between devices. If you're buying new devices every couple months, of course you're not going to see a difference. But going from year to year, the difference is noticable, either in terms of operational speed, camera quality, or battery life. What you won't see is the difference OEMs and hardware partners claim. The difference is noticable, but not twice the speed or battery life. As with anything the improvements are gradual, but it's not to say that they aren't there.
My final point is my suggestion for people buying multiple devices a year who are considering switching to one device for multiple years. While I understand that many don't keep every device and sell of their old ones, you're still going to have the initial cost of a device plus the amount lost each time you sell an older one. Buying a new one every couple months, the cumulative losses you incur selling old devices plus the cost of the device you currently have would probably be equal to 2 phones, if not more. By just picking one device per year, you would've already halved the money spent of devices. Now obviously keeping a device for multiple years drops that even more, I was simply suggesting that instead of making such a radical change from one extreme to the other, split the difference and take a more moderate approach. And so no one mistakes what I'm saying, I'm not telling anyone what they HAVE to do, just making a suggestion. It's your money after all.