I'm of opinion hail stall is overpowered. Sure there are counters to it, but even so breaking its multiple walls is hard. Hail stall typically has multiple copies of Protect, during which your poor wall-breaker will be taking Hail damage, and then there's the infinite Substitute / Protect Walrein chain, and woe be to you if you get hit with Toxic or get poisoned from Toxic Spikes / Poison Point! Hail stall has its weaknesses, and the weakness to Stealth Rock really helps. But I think the counters are a bit too hard to use, and having to force a Pokemon like Clefable into your team just to take out Hail stall, well that's going too far.
Personally I'd prefer moving Snover to BL; the permanent Hail is what makes Hail stall works after all. Unfortunately removing Snover will kill Hail stall. Otherwise I dearly want to say Froslass is broken, but then again in my experience she's not that bad. Fast yes, Spikes yes, blocks Rapid Spin yes and has Destiny Bond. All this makes her a good support Pokemon. But I can't rightfully say I've had much trouble with her. Snover yes, but not Froslass.