If the end effect of security is dropping packets NAT and Firewalls both in effect drop packets.
Its kind of just silly pedantry to say NATs aren't security because sure you can't do things like block specific ranges of IPs spamming you (or make outbound rules to control local devices) but 99% of people don't need.
I understand ipv4 networks pretty well. And I would say that any device doing NAT is acting as a basic firewall. Do “true” firewalls do more? Sure. But saying NAT doesn’t provide security is flat out wrong.