As the ultimate cause is a bad design where they have underprovisioned the battery with little margin for degradation, presumably in order to fit it into a thinner phone, it becomes Apple to handle the issue in a transparent way. The right action for Apple then is not to degrade the performance to hide the problem under the rug, but to make it clear to the customer how they can have the phone serviced in order to make it work like before.

Apple is so lucky that this got noticed and they got called on it. The alternative is that millions of customers would continue to get an inexplicably bad user experience, which would chip away on their reputation in a more indirect but not less dangerous way than facing the press.