I'm astonished everyone seems to be ignoring Apple's true intentions here. This is not about performance or specifications - as that has been disproven in this article. You have to put yourself in the position of the normal, average user. Apple's playing a psychosocial game.
The average iPhone user uses iMessage. Whenever they realize they can't edit messages or take advantage of the new features added to iMessage on iOS 16 (which their devices could easily support if Apple's intentions were any different), they'll get socially pushed to upgrade to a new phone.
Additionally, the lock screen is the first thing you see on a phone. Whenever users with a 6s or 7 see that they can't edit their lock screen, they'll be impulsed to buy a new phone.
This is what Apple wants. They are very smart.
They've also done this before - with emojis.