Re: iPhone 6 and iPhone 6s are different things
The iPhone 6 (and 5S) were only "dropped" from NEW iOS releases in 2019. They are still getting security updates to their latest OS, iOS 12, to this day - almost 8 years now since the 5S first shipped.
The thing that makes a phone become obsolete is having security updates stop. Not getting the new features from a new OS (some of which require newer hardware so you couldn't use them anyway) doesn't make the phone any less useful, it just stops becoming MORE useful.