He has great political popularity and charisma, managing to gather up many, many Orcs that follow him without question, lead the Horde to immense prosperity and power (yes), through excessive force and slaughter, being successful in most instances against his enemies, being physically strong enough to overpower Taran Zhu and Thrall barehanded, and many others with ease, and finally, managing to take perfect control of Sha Energy, and using it to successfully bring chaos and destruction without really implicating himself at all, as he was perfectly fine after his defeat. All of these traits and deeds, for what they are, seem to imply Garrosh has become one of the strongest Orcs to have ever existed, and I don't think I've listed all of his notorious deeds either.
What do you think?