Blizzard has played it very conservatively with overload, generally. Totem Golem is probably as far as they've taken it. And it's a fine card imo. Its only problem is that it is built to answer 2/3's and 3/2's and nobody really plays those in Constructed on Turn 2 right now. It's all about Shielded Minibot, Haunted Creeper, Mad Scientist, Wyrmrest Agent. About the only thing Totem Golem can handle is Knife Juggler and Darnassas Aspirant.
It feels like Blizzard's design team is made up of several different people who work on cards by themselves separately and each person has equal say on what goes into the game. So what happens is that one person makes cards to balance out a meta, and then another person goes and makes changes that makes those cards completely useless. The biggest example I can point to is the nerfing of Gadgetzan Auctioneer when they also release a ton of anti-spell cards at the same time. In the same case with the Shaman TGT cards, I think someone made Shaman cards to carefully give them a fair boost over the GVG meta but did not look at all the other cards that were being designed so they still end up underpowered at the end.