Exactly. There is no reason that a network supported by masternodes would be less secure than POW. Masternodes are already more decentralized than POW block finders, and if a change away from POW were to happen, there would be a multitude more masternodes added to the network because of the added profitability of owning one, even further increasing the level of decentralization.

Full disclosure, I am a miner AND masternode operator. I would continue to mine other coins in order to buy more masternodes