When a newer model is released, that should indicate that the previous phone is no longer the flagship. The latest phone(s) that take over is considered a flagship. The iPhone 6s was the flagship for 2015 up until the iPhone 7 line got released. Then the iPhone 7 line took over as the flagship line. Just repeat that cycle for the iPhone 8 and X and any later devices.
Again - I never mentioned iPhone 6s YOU DID.
You just keep making up new arguments that aren't there.