a PT doesn't need a cotank on the foreman who crushes.
Neither does my Shadow, nor have I ever needed a cotank. Playing a Shadow requires you actually know how and when to use your abilities rather than simply faceroll the keyboard and expect things to be dead when you look up. VG/PTs are completely idiotproof. *Anyone* can play a VG/PT effectively. You (and probably many other people with a bad opinion of Shad/Sin and Guard/Jugg tanks) are probably used to dealing with people that would be better suited to VG/PT tanking than a class that actually requires some foresight and skill. I've never had a problem on any of my 3 tanks, but I've *always* been told that my Shad/Sin is the better threat generator, damage dealer, and damage mitigator, and pretty much all of that comes from the fact that I know the class and content backwards and forwards so that I can actually use all of my abilities effectively.