do you have to "learn, document, configure, and patch" a firewall on ur home router? most ppl just plug it in bc it's configured to work.
Home routers have gotten pretty good about sane defaults these days, but at a minimum I'd be disabling UPnP and looking over what those defaults are before trusting it to protect my network.
You could argue that having one edge device running a checked and configured firewall means that you don't have to worry about the firewalls installed on every other device on the network, but anyone who has networking experience will know better. Problems are bound to come up on the internal network if nothing else and troubleshooting issues becomes a lot more complicated!
Also, if we're counting on every IoT product to come with its own embedded firewall you can be sure many of those are going to be so poorly thrown together that they introduce more security problems than they solve. This is a class of products that has earned a horrible reputation in terms of security.