Pretty much any card nerf discussion has sparked heavy debate and resistance where I'm surprised a large volume of people no matter what the card was have claims that they were blantly broken or weren't overpowered. it's not very black and white either, even cards like envenom from alpha, 0 mana unconditional backstab, 2/3 defias ringleader, 2 mana unleash, under taker or the classic defender of argus had heavy resistance to being nerfed. After reading countless pages of debate on Dr. Boom being Op or not, nat pagle being Op or not. Thaurassian is just the new card to debate about. I'm starting to question what I thought might have been OP really was if so many people truly back blizzards original concept maybe I'm not very savvy at spotting what is over powered as I once thought I was, has there ever been an over powered card?
Dr. Boom is so good that basicly everyone uses it, even aggro decks. Just like 5mana Sylvanas. And everyone runs also a BGH because of that. Can't see why blizz doesn't nerf it, maybe because ppl paid gvg packs for it.
Now my criteria for a card being overpowered is very narrow. A card being super popular seems to be equal to a card being overpowered in the minds of a lot of people. Dr. Boom is the best example i don't actually think the card is overpowered but it's played in nearly every deck and while many people tend to scream "overpowered" because of that it is - in my mind - simply related to the fact that the card lacks competition, if there are no other good neutral 7 drops then the one that is good will obviously see a shitload of play.
Other cards like Undertaker or even pre nerf Warsong Commander are a different story, these were either much better than every other option you could possibly play or enabled some stupid and OTK decks - leeroy getting an honorable mention here - and those are the cards that need nerfing and can be considered overpowered in my mi
If a neutral 7 drop is blatantly better than most 8 drops (including class 8's) when disregarding mana. Then yeah, there's a problem.
If you look back at the history of nerfed cards I think you can see why Blizzard are so circumspect about making changes to BGH and Dr. Boom. Now that the pool of cards has grown and there's been a little power creep, some of the nerfs seem excessive in retrospect. Cards like Shattered Sun Cleric, Tinkmaster Overspark, Nat Pagle, and Starving Buzzard have disappeared from constructed play completely and others, like Undertaker, Leeroy Jenkins, and Defender of Argus, are now very niche cards.
Not only were some of the nerfs really harsh (Tink and Buzzard especially), but some of the cards weren't really overpowered—they were just too popular. At least two of them were honest-to-God OP: Tink completely trivialized other legendaries (especially those with deathrattles, like Tirion and Sylvanas) and Undertaker just created unwinnable games for opponents. Shattered Sun Cleric and Defender of Argus, on the other hand, got nerfed because they were ubiquitous in zoo decks—but if they were restored to their pre-nerf stats, would zoo make a comeback today? Probably not. Pagle was nerfed because he was in practically every non-aggro deck, but now that more card draw options have appeared and the game has gotten faster, would pre-nerf Pagle still be a problem? I doubt it.
Dr. Boom and Emperor Thaurissan are just a little cheaper than they "should" be. We might see them tweaked the way Sylvanas was, but we might not, and they don't really need to be. They're very good cards, but their only crime is being popular (and I think we'll see Thaurissan drop out of most non-combo decks in the coming weeks anyways). Eventually, as the game grows, other strong cards will arrive and, to some extent, displace them. BGH, on the other hand, is broken in exactly the same way Tink was: it trivializes an entire category of cards, and the problem is only going to get worse as the game grows. Every new minion with 7+ attack will be judged in relation to this one little 3-drop. That is a disruptively overpowered card.