That is only a half-truth. Apple controls the key infrastructure; they may replace your keys with arbitrary ones at the demand, coercion or compromise by any number of bad actors. The software is closed source, making it impossible to verify any actual claims made otherwise. If they truly valued privacy, why not open source iMessage, allow users to verify iMessage keys, hire an independent third party to audit their infrastructure, or all of the above?
Moreover, Apple has moved iCloud infrastructure to Chinese data centers to enable spying on millions of innocent people. They have removed apps from their store which circumvent Chinese censorship. These are truly shameful acts which has appropriately drawn criticism from human rights watch organizations.
https://techcrunch.com/2018/02/25/apple-moves-icloud-encrypt...
https://www.cnbc.com/2018/02/24/apple-moves-to-store-icloud-...
https://www.nytimes.com/2017/07/29/technology/china-apple-ce...
https://blog.cryptographyengineering.com/2013/06/26/can-appl...