2% does seem quite low, but remember this isn't 100% accurate. Also remember the majority of players will continue to work on it over the next few weeks with Flex / LFR, and the number will shoot up.
I will admit that Garrosh is a step up of all the bosses, but I quite like that, and I hope they keep it that way. Garrosh feels like an exciting encounter, I really enjoyed downing it and even on Normal Mode, I got a rush from killing him. I really look forward to the battle to Heroic Garrosh, but I suspect they'll do an Icecrown Citadel Buff or a Dragon Soul Nerf over time.