If you can actually catch a rogue, chances are he's dead.
A Warrior is pretty powerful overall and any of the caster classes have the ranged advantage.
Hunters may not be particularly strong, but an explosive shot would probably hurt a lot and *insert tamed animal bite here*
Monks can endure much punishment and can drink themselves to better health or more resistence and are pretty defensive so they are a little bit above Rogue, maybe better then some warriors that don't use shields.
Druids have a huge connection to the natural earth and spirits so they can harness a lot of magic, the problem with that is that there are some evil spirits or other entities that easily manipulate druids. If it is any other class in lore that is susceptible to corruption its either Druids or Priests since the 'shadow' can corrupt the light.
Which makes me believe the weakest class, is priest. They have a great attachment to light, that can be extremely valuable but their closeness to Shadow is too great and can be easily manipulated or controlled(incoming Anduin turn btw) that are unlike the Paladin class which is all about purifying darkness.
Death Knights are powered by undeath so that's a powerful undertaking already to be able to control a plague.
Shaman's have the elements which while are also pretty corruptible but have good intentions for all of Azeroth/Dreanor.
Overall I think Priests are the weakest, sure Shadow and Holy powers are strong but that shadow magic is unpredictable and very easy to corrupt or manipulate which makes them seem like a pushover(Benedictus and Anduin are pretty good examples, as one was corrupted entirely and Anduin's attachment to the light was heavily manipulated in MoP.