Yes, you can normally build decks around everything - there are decks that target specifically Big Priest … and lose against everything else.
Just because you can build around it, doesn’t mean it’s ok. Why should I take a lecture and tech my decks against other player’s deck that they just copy-pasted from the internet?
I had two games against control warrior today and both times they played Dr. Boom and both times it was just a HORRIBLE experience. Even if the card was statistically not relevant (it is, it really is) this legendary hero alone makes me wanna quit Standart right now. There is no way that giving all your stuff rush is ok for 7 mana. The card has no counter (you can’t even negate the card somehow) and adds crazy hero powers and 7 armor on top. How can anyone seriously defend it?! I’m really baffled.