The comparison between a statefull firewall and NAT is often because they feel like they are doing the same thing from a mechanical point of view.

For example here is how to achieve the same result in PF, note the single additional operator needed to specify nat.

block in on $EXT_IF

#NAT

pass in on $INT_IF to any rdr-to $EXT_IF

#statefullfirewall

pass in on $INT_IF to any