OK, so there's an attacker on the network in both cases (UXSS and the worst-case-dnsmasq-vuln). So, to compare the two, you look at what else you can do -- and UXSS clearly wins there. "It wouldn't be hard to mount a phishing attack" -- maybe? Except on the most valuable phishing domains, which already have HSTS -- and the UXSS alternative is that I literally control your browser which is clearly worse since I have almost definitionally attained the goal of the phishing attack! And if I really want to just steal your password instead of just using your session, I'm guessing "full control of the DOM everywhere" will help with that.

I have also already argued that an extension does not need to be malicious -- just buggy -- to get UXSS.