To clearly see the lie around here, Apple says the issue comes from unexpected shutdowns in iDevices because the battery couldn’t keep the load to power the CPU. So, the battery is defective, but they wanted to hide that by reducing the clock speed of the CPU so it won’t use that much power and they don’t have to apply warranties to the users.

I don’t know how is a good user experience that as soon as my iPad upgraded to iOS 11 it became super sluggish while in iOS 10 was kind of fast. To me that is not a good user experience. No mention that downgrading to iOS 10 is not a super simple task.

A nicer user experience is letting the user know the battery is faulty, and because of that the user should take the device to maintenance. I have never experience sudden shutdowns in my iPad but is super slow (most noticeably in the keyboard). Why it must be underpowered?

• Early in 2018, we will issue an iOS software update with new features that give users more visibility into the health of their iPhone’s battery, so they can see for themselves if its condition is affecting performance.

So… As far as I understand, Apple won’t let you disable that “feature” of under clock the CPU in order to hide the battery age. But you will know if your battery if faulty and Apple is doing “the right thing”.

Source: A Message to Our Customers – Apple