Apple did not slowly degrade the user experiebnce over time, they throttled the cpu in order to prevent the phone crashing due to a old battery, do you think that a phone that crashes sporadically is a better user experience?

As you state it is an issue of consent to this throttling, if it was communicated effectively this wouldn’t have been a ‘Gate’.

A good way described in a podcast (think it was Rene Ritchie on the talk show) would be to let the phone crash then pop up a message with an explanation of what’s happened, that the phone is now dialled down to prevent future crashes, you can turn it off in settings etc..