Dory isn't broken. It has a number of counters who are also viable in the general metagame, and it doesn't have the movepool or stats to play around said counters. Gliscor will always beat a Doryuzuu barring rock slide flinch hax. Bronzong won't lose to dory either.
For the same reasoning, Darkrai, Deoxys, and Skymin are broken. There aren't any pokemon that counter them while still maintaining general metagame viability (would you really be using primeape in ou if it weren't for darkrai?). Techincally, deoxys has counters (SpD Rachi, Scizor), but the ability to ohko over half the metagame with one set is insane. And scizor loses to sub + fire punch.
For the same reasoning, Darkrai, Deoxys, and Skymin are broken. There aren't any pokemon that counter them while still maintaining general metagame viability (would you really be using primeape in ou if it weren't for darkrai?). Techincally, deoxys has counters (SpD Rachi, Scizor), but the ability to ohko over half the metagame with one set is insane. And scizor loses to sub + fire punch.