Shaman wasn't the only class that got strong cards in karazhan. Before karazhan, hunter was already one of the strongest classes and they probably got the biggest buffs. They got cat trick, grandma, cloaked huntress and barnes. Zoo got malchezaars imp, silverware golem. Spell druid got arcane giants. Beast druid got raven and warden. Mage got book, valet(not as strong as right now with arcanologist but saw plays in aggro freeze mage which was one of the best counter to midshaman) and firelands portal.

They could have printed some shitty cards for shaman. Shaman would probably be still fine(like tier 2) with a strong core that consists of trogg, totem golem, flametongue, thing from below. Not having spirit claws and portal would weaken their matchups against zoo and hunter. As a result, those decks would probably replace mid shaman as the best decks. In an alternative timeline, people would be complaining about why they printed strong cards for hunter and zoo when they were already strong.

Right now according to live meta tracker, the strongest decks are aggro token druid(mid token druid has its own category), pirate warrior, murloc paladin. Pirate warrior barely runs any new cards(maybe one phantom freebooter). Some of the highest winrate murloc paladin lists run righteous protector, bonemare and lich king(last 2 being neutral minions) as the only new cards. Aggro token druid lists dont run ultimate infestation or spreading plague. In fact, many top legend jade druid players ) also dont run spreading plague.