Re: "To provide a better experience to customers"
It's a good idea to limit the processing speed if failing to do so is liable to cause the phone to shut down. Slower overall processing beats no processing.
It is a terrible idea to do that without telling the consumer and, when the consumer comes to one of your shops to diagnose their slower phone, not tell them that they can just spend X on a new battery, instead recommending that they spend ~10X on a new phone.
I feel like what Apple did on a technical level is correct; what Apple did in terms of communication and sales is a pretty terrible thing. It's easy to believe that a lot of people will have given Apple money that they would not have, had Apple provided the missing information. Which feels like valid grounds for a lawsuit to me.