NAT's firewall effect is purely coincidental. In fact, because people don't run firewalls because of NAT, attacks like NAT slipstreaming can open any port to any internal IP in your network by abusing SIP ALGs and fragmentation.
Wherever NAT is enabled now, a statefull firewall is a better solution. Thankfully, this is the default wherever IPv6 is rolled out to consumers.
Wherever NAT is enabled now, a statefull firewall is a better solution. Thankfully, this is the default wherever IPv6 is rolled out to consumers.