It may be that Nxt is in fact 100% secure because >50% of the stake has always been held by a few people such as Marc De Mesel who will defend it against attacks. That doesn't make it decentralized nor does it make the method secure just because Nxt in particular might be.
I guess you have to ask yourself, "How much does decentralization matter if the currency holders are the ones that secure the network?"
It certainly does. The point of cryptocurrency is not Moon. The point is to have a system of enforced rules where all participants are protected not only from outside attackers but from each other.