Well, I can understand you're reasoning for that, and I respect that. I think it's obvious that you're not changing you're opinion on this, but I'd like to ask a legitimate question of you before I drop this.
My question, which I believe I have mentioned about three times now yet has gone mostly unanswered, is why is Kyurem-B A-Rank? Perhaps I'm missing something here, but all the flaws you listed that keep Hydreigon out of A-Rank seem to apply to Kyurem-B too. That list of common OU pokemon that threaten Hydreigon? Those scare off Kyurem-B too; it has that same Fighting (and Dragon) weakness that you deem to be so crippling. Slow speed? Kyurem-B is slower than Hydreigon, making it susceptible to the same faster threats, ironically including Hydreigon. On top of that, unlike Hydreigon, Kyurem-B is weak to Stealth Rocks, in addition to all other hazards (Remember, Hydreigon has Levitate; it's not hurt by Spikes/Toxic Spikes). That means that, in addition to being hard to switch in in the first place, due to it's slow speed and weaknesses, it gets badly hurt every time it does. Oh, and it's also weak to Bullet Punch, so the #1 most common pokemon in OU threatens it.
I suppose what I'm getting at is that Kyurem-B might be more suited to B-Rank. It has all the flaws Hydreigon has and then some, so unless I'm oblivious to some EXTREME advantage Kyurem-B has, I think B-Rank might be more fitting. If I am overlooking something, feel free to correct me.