There is no situation in magic where someone buys a recently released card and 2 weeks later the card is banned.
Yes there is, wtf are you talking about? I mean, sure, it might not be 2 weeks, but sometimes they do ban cards just because they're too good (ex: Jayce the Mind Sculptor). It just doesn't happen very often because they have over a decade of experience in card games, unlike Blizzard. And I'm not sure you realize people get to disenchant nerfed cards for the full dust price. But the biggest issue here is game balance. Game balance should be above all of that because a game being blatantly unbalanced completely kills it. It's really naive to think no cards will be changed now, especially after new cards come out and we have a new metagame.
Also, let me leave some statistics here to help you decide if hunter is OP or not:
Hunter has the 3rd highest w/l in constructed. Above him are Warlock and Druid.
Hunter has the 6th highest w/l in arena.
Hunter has a "negative" w/l vs 3/8 other classes. Druid has 2/8 and Warlock 1/8 (yes, on average Warlock only loses to one class and wins vs anything else).
Anyone who wants to make generalizations about Hunter winning vs everything and having no counters should maybe look at other classes first.