Re: Unscientific anecdotal sample
"However, a mate of mine who's been drinking at the koolaid fountain for a while says that older phones generally struggle on newer releases of the OS after a few years"
Never noticed this, and we've always had older iPhones in the family. My 11 Pro is as fast as it was new, in fact if the camera was a bit more up to date I wouldn't be thinking of replacing it. The only one that's truly slow these days by today's standards is the 5S, but that's been out of support for years now and it has a dying battery which no longer supports peak performance.
"many apps insist on the latest version of the OS"
Some secure apps such as banking do indeed ask for the newest (or newest -1) version of the OS, but most will let you go back several generations. And given that it's typically 7 years or thereabouts before the newest OS stops being supported, this is not generally a problem.
"...and use changes to ask for new licences"
Not a thing, and never has been as far as I know. Sounds like a bit of FUDraking to me.