While you're not wrong about the complaint for the price and the age of the device. The iPhone 6s is still receiving update, though it may not be long for this

While you're not wrong about the complaint for the price and the age of the device. The iPhone 6s is still receiving update, though it may not be long for this world, the iPhone 7 and 8 are still one and two years newer than said 6s - as such would likely receive updates a year and two years additional. That would put the iPhone 8 End-of-Life at 2024. That's 2 years out, and the 6s hasn't even finished receiving updates, so closer to 3 years out.