We're talking about different threats. Any OS can potentially be rooted, including a Live OS, including Tails. An attacker with root access can disable Tor, iptables rules, and transparent proxying. An anon middle box as a separate physical device protects against that. Of course, if you get rooted, you can be fucked in many other ways, like the attacker reading sensitive files that store passwords or customer info, but your IP address and location will still be safe with a middle box. Obviously, you should never store personal info on the dirty computer.