Apple didn't hide it. It was in changelog of some iOS version. They just didn't make it a big deal. Honestly I don't think that this is a big deal. Today's iPhone is absurdly powerful. This speed is not needed for average user, so he won't notice this downgrade.
It's a pretty hollow defense, because users are clearly not reading changelogs, and a reasonable person would obviously understand that a consumer's response to a poorly performing phone is conclude that it's time to buy a new one.
And my understanding is that there is no explicit mention in the changelog, just an opaque mention of new power management feature. But again, no one reads changelogs and the folks at Apple know that.