What??? We're talking about the current iOS updates, not next year. They've been doing it since iOS 10. By the way, they would not have addressed this issue had they not been caught doing it.
So they increase the battery life by making your phone run like crap. Now you think your phone is running slow so now you want to buy a new phone rather than tell you that you have the option to replace the battery so it'll run like it did before. Pretty good plan by Apple to get you to buy a shiny new fast phone.
An old battery with a full charge in a couple of hours will reach the critical point where the iOS will slow it down to avoid the shut down, but by doing that the phone will become useless. I don't think that's a solution at all because that will give the impression that the problem is the phone an not the battery...