NXT's security in the bootstrapping phase (before Transparent Forging is implemented) is similar to Bitcoin's, it can be 51% attacked. Transparent Forging is supposed to fix this flaw in NXT. However, in Bitcoin this flaw will remain unfixed forever, as miners will never agree to change status quo and will keep things running as they are now until Bitcoin becomes obsolete with other systems that actually move on with development. Not necessarily NXT, it could be something else, Ethereum or whatever.
Stop claiming its a Myth then. You should at least wait for a completed whitepaper and release of source code that is properly digested by security researchers before even suggesting Nxt is secure. To not do this is misleading and dishonest.
The most you should claim is that perhaps in the future some PoS algorithm can solve the NaS problems.
Additionally, it is indeed very well conceivable that miners will accept a hard fork introducing some other security mechanism instead of just PoW. If they are properly incentivized they would happily stop throwing away most of their profits into new asic technology. Perhaps a variation of bergstake, perhaps a variation of slasher ghost, perhaps PoR will be introduced into Bitcoin as a merged security mechanism. Until these fancy new toys get properly peer reviewed and tested, suggesting bitcoin migrate away from PoW is irresponsible.