Claiming an argument is disingenuous because you don't like it is an extremely cheap retort. They clearly were sincere in their statement, and given that the 6S was released in 2015, everyone who bought one at a later date knew that it was an older device, and it's still supported and will continue to be supported.

Another way to put it is that no one does better than Apple at keeping their devices useful and valuable (easily demonstrated in resale values). Maybe Apple could do even better, but it's in a market where it is far and away the standout.

As an aside, people say "well look I can put some completely unsupported, random ROM on my old device!" is not a counterpoint. iPhones and iPads continue on as our kid's devices, resolve for a handsome resale price, etc. Competitor devices collect dust in a drawer. This is empirical truth.