Hmm. I hadn't seen this brought up and I think it's a stronger argument than most others.
The IPv6 equivalent is services on ULA only, but that's not a default behaviour.
Consider what would happen if you have NAT but your firewall "doesn't work", would the ability to route packets to addresses in your local network act as an extra layer of protection in this case, as you imply? Absolutely not, since your router's IP is still clearly exposed to the internet, and without a functional firewall they can just remotely connect to its configuration interface and change your network topology as they see fit. Ultimately at the end of the day, anything that could reasonably compromise your firewalls capabilities can equally work around NAT.
Not to mention that unlike IPv4, in which the address space is so small you can feasibly brute force the entire local address range to discover any open ports in the event you compromise an internal node past the firewall, with IPv6, the address range becomes so large, bad actors must resort to alternative more complicated means for mapping the network topology.
Ofc neither matter in the end if your router gets compromised. The only reason so many people believe NAT protects them is because they are "buying" into the abstraction more than they are about the physical reality of how these systems are built & function.
The point is not that "it can", the point is that on ipv4 "it doesn't work without".
In order for ipv4 to work at all you MUST use NAT, and implicitly a firewall, those two always work together even if there the person installing the system doesn't know the word "firewall", which is usually the case.