[throw0101c]

> In my opinion, NAT was an added layer on top of firewall rules because […]

… there were not enough IPv4 addresses to go around, and so you only got one, and if you had more than one system at home, too bad… until NAT got invented.

Back in the dial-up days, you had only one system connected to the Internet—the one that was connected to the modem—and it got the the IP address directly. It was only later with the always-on nature of cable and DSL ISPs that sharing a connection became a thing. IIRC, you used to connect your computer directly to the {cable, DSL} modem without an intervening router, sometimes using USB, as computers having built-in (Ethernet or Wifi) networking wasn't really a thing:

* https://support.dlink.ca/ProductInfo.aspx?m=DSL-2320B