I doubt that this is true. Can you point me to where you heard that?

You should probably think carefully and make up your mind whether decentralization or 51%-attack-resistance are more important to you:

https://bitcoinmagazine.com/articles/zcash-creator-on-the-upcoming-zcash-launch-privacy-and-the-unfinished-internet-revolution-1472568389/

(Search in text for "fundamental trade-off".)