But my 70yo mother, who is pretty far from being technologically savvy, uses continuity every day to copy one-time-use codes from her phone to her computer, even though she'd have no idea what the term "continuity" means in this context. She notices that it's easier to snap better pictures in more conditions than it was a few years back (and that pictures she receives are better looking on average, too). She uses 1Password with FaceID, which I set up for her, because it's so easy to just look at your phone to unlock that there's very little in the way of enabling and using that, and she doesn't need to write down passwords anymore.
I think some of the magic of the Apple ecosystem is that you don't have to know about these things in order to use them. Someone shows you how to do something (Apple could certainly improve on the organic discoverability of many of these features! Some are impossible to find without looking), and then it often just works. And these things do keep getting closer to that ideal over time, with each generation. When I first started using continuity — long before my mother did — it definitely did not work all the time, and I persisted because I'm a techie early adopter. Eventually, though, it reached a state where once folks learn about it, they can just use it.
I'm also not sure about the 3-4 year number, at least from personal experience, fwiw. We pass down phones in my family, and it easily takes 5-6 generations for them to reach the end of that chain and be in use for a year or two before they're switched out for the next model. Battery has never been the reason someone in that chain switched phones.