No, it's complete nonsense. NAT just happens to serve as a form of firewalling in IPv4 land because usually, the stuff behind your router has a private address

No, it's complete nonsense. NAT just happens to serve as a form of firewalling in IPv4 land because usually, the stuff behind your router has a private address. Proper firewalling is a matter of policies; it's completely orthogonal to whether your devices have a globally routable address or not.