Any PC with a NIC is one VLAN and masquerade rule away from being a router

That is true, but you can also add USB Ethernet interfaces to any PC, which is even simpler.

For example, my router/firewall, which also implements various other network services, e.g. hosting my own e-mail server, is an old Intel NUC with 5 Ethernet ports, 4 of which are made with USB Ethernet interfaces.