Again for me, while it's offensive coverage is good, it's really outclassed by Latios and KyuB for offensive dragons. Latios' important 110 speed tier, mixed offensive STAB combination, and Defog allow it to perform as a better offensive Dragon while also offering hazard removal, and can arguably handle Stall reasonably well with a Trick set. Meanwhile Kyurem-B's offensive stats and ability just render Hydreigon obsolete in this role. Who cares that you have a SR weakness when their SpA stats have only a 5 point difference but Kyu-B has a whopping 65 point advantage in attack? Their speed is roughly the same too, both between important milestones and Kyu-B can run Leftovers while Hydreigon runs LO and hit far harder on average on both spectrums. This also means its a much better scarf user too.
But again, that's why I like capitalizing on its niche in defensive typing, good support movepool, and ability to recover and use U-Turn. Dark has great neutral coverage as a mono-STAB, and a second coverage move is all you need to take out the threats you want for the rest of your team. It's a good pair with Mega Manectric as a Voltturn duo for example.