The reason I say 2 that do the same job is positioning and movement. For instance on Gruuls you will need to avoid the caveins on both chars. You can watch one screen and move them together. Also with Leo, Al'ar, void Reaver... If you are just standing still then ya you can do any 2 classes, but if you want some combo that you can take into any 25 man, then you need to be doing the same thing from the same postion. That's just from my experience.