Agreed with the main message.

... but

An incoming message to an IPv4 NAT router will not be forwarded to a LAN device unless it matches a known flow (typically continuation of a conversation, typically initiated by the LAN device, which is expected), or the user set up a DMZ forward to a particular destination. There is actually no reasonable way for non-DMZ LAN devices to be exposed to the noise.

For non-NAT IPv6, sure a firewall might be on by default, but it can be turned off - and therein lies the potential exposure to every LAN device to directed traffic.

In other words, the risky zone for IPv4 NAT tends to be setting up a DMZ exposing 1 device, while the risky zone for IPv6 non-firewalled tends to be exposing all of the devices behind the router.