Thunder 2 I dont have set on my hotbar. I think no one will argue that this one is absolutely useless once you get T3 for procs.

Aetherial Manipulation, definitely use it more. It's a great skill.
Lethargy, good for the heavy. It's utility that actually sees (rarely) a use in raids. I think A8S with slowing down balls is the latest example.
Sleep is useless for you if you don't pvp. Blizzard II can be mainly replaced with Freeze if you don't pvp. Virus is also rather useless if you don't pvp but it can find a use every here and then but in 0.05% of the cases it's gonna be an actual deal breaker I guess. So, useless.

Definitely keep Blizzard. It saves you from screw ups. It can also find a use as filler when you try to recover MP during UI and you happened to T3 proc before going UI3 AND have a slow MP tick. Or if you simply want to draw out your UI3 because of the fight or something. Niche but definitely has it's uses.