The PDex is decentralized and spread out across the nodes. So I don’t believe it’s dishonest marketing to say PDex is decentralized. Here is a good article about how it works.
So I think the reddit user is really critizing the coin shielding mechanism, which utilizes the burn and mint mechanism to shield and unshield coins.
The reddit critic says you’re sending your funds to a custodian and getting an IOU in return. For example, if I shield BTC, my original coin gets sent to the burn address (the “custodian,” if you will), and in exchange I receive newly minted pBTC (the IOU).
I don’t know, maybe to a certain degree the critic has a point, but I think they might be overstating that point, drawing broad generalizations, and coming to extreme conclusions based on a few logical fallacies.
That said, I’ll let someone else here who knows more about the system speak on its behalf.