So it seems to freeze only melee attacks, what a shame. Anywhoo, What level should it be in, now that it’s more meh than wow? Cryo3 askin here- 
I think it’s still good to max or cataphracts will rush you to death (or any other multi-hit melee skills). It’s still one of the good defensive skills wizards have.
You got Sage now, ahaha. It’s got huge nerfed, but not really become useless.
Cataphract need to watch-out your subzero shield
And some deadly melee attack
Swordman is very good on Rank 8, Subzero Shield might be very important then. I’d keep it at 10 since it’s still OP against meelee targets. Also there’s not really a point in maxing other Cryo skills.