If you're happy with what you have then of course you can make that decision to keep using it. But I can assure you, you're missing out on a ton of great stuff by using an ancient device. iPhones are supported for a long time, but the intention is you should upgrade every couple of years or so.
New features are great, and I enjoy them, specially the ones that interact between devices across the ecosystem.
But I primarily use Apple products for their intuitiveness, very easy learning curve, stability, and rock solid like (up to a point) software.
I´m well enough and I live a quite comfortable life, but I´m not rich. Apple products allow me to buy them and them use them without having to worry about anything else for a very long time, like my refrigerator. I buy them when they come out and then use them through their entire life cycle. Then, when they stop being supported (software wise), I buy the next generation that is released. This span of many many years implies that yes, at some point during that life cycle, some new features wont be received by them, even though the are still being updated. It does not matter to me.
This were features that I didnt have yesterday (because they didnt exist), and I can continue to live without them after they are being unveiled to the world until I buy a new generation of the device.
This have another positive (in my view), outcome: Because I renew my Apple devices after so many years of use, the change, both in features and in performance, is DRAMATIC every time, which it isn´t the case if you upgrade every year of every couple of years.