You'd still need the router to tag/untag those VLAN's and allow traffic to flow. So if the router does VLAN tagging but just routes between the different networ

You'd still need the router to tag/untag those VLAN's and allow traffic to flow. So if the router does VLAN tagging but just routes between the different network segments you haven't fixed anything. You'd also need a firewall, and to configure it correctly.