I am not arguing the "what if". I will not pretend to know the reasons or lack thereof for cutting support. And frankly, I do not care, as I do not own an iPhone 7, or ever have.Sorry, but all I can think of in response to your post is laughter.
But I will try. You know perfectly well that Apple can easily introduce ios 16 on iPhone 7. Will it have limited functions due to older technology? Yes of course. Like the iPhone 10, it does not have everything that the iPhone 11 and 11 have everything 12, and 12 everything that is 13, etc. It's about the fact that the iPhone 6s for some reason is privileged over 7. This is a dangerous precedent because you have no warranty at Apple for the obvious fact that a younger device is supported longer. And no matter what generation of the iPhone we are talking about.
I'm simply pointing out the sad excuses for "arguments" certain individuals have for the hypothetical or actual people that purchased an iPhone 7 in 2019 crying about lack of software support for 6 year old device, regardless of when they as a consumer actually purchased the device.