You miss the difference between a system that cannot reveal anything of worth to a third party because the privacy is done at the protocol level and one that must have a certain number of human controlled nodes
If you really think a masternode operator can unravel the blockchain history systematically and to any practically useful extent then that is a very different proposition from saying masternodes are centralised.
I doubt thats remotely possible even now - never mind after a further year's worth of protocol hardening. Feel free to try it if you even know where to start. I don't think you do.