First, it was one of the top 10 coins at Coinmarketcap when the Ethereum rally terminated because of the DAO fail. Further, it was one of the coins that didn't have to do anything with the "Smart Contracts" and "DAO" buzzwords. Lisk, for example, was affected by Ethereum's decline because it has many similar properties.
You don't suddenly get 100X Monero's volume without a manipulator. Don't fool yourself with nonsense.
Second, NEM does quite well with marketing. It may be debatable if Proof of Importance is a real innovation regarding to Proof of stake, but it sounds good in their whitepaper. I think that Proof of Importance does have some properties that are favouring some crypto business models (like marketplaces and gambling activities) that small altcoins need to grow. Also it seems to have a pretty successful side project (Mijin), a NEM fork for banks and other companies.
There is no debate. Only n00bs who don't understand that there is no debate. I already explained the technical reason that PoI is just a way of doing PoS and fool some n00bs into thinking it is an innovation.