"It's a 7 second silence and interrupt which also happens to do pretty decent damage. It's hardly a weak ability and frost is already pretty competitive."
It only does damage if you have used all your skills to apply debuffs.
If I do: Rain of Ice, Frost Nova, Deep Freeze then I've done several hundred damage with Freeze, but now I'm also destroying all those -movement speed debuffs that I've put on you, so when I back up to try to kite, you can chase me easily (if that's what you want...)
If you used Frost Nova, then if I'm melee or kiting range which means:
Reg I've already mined and used Betrayer
Torch I've used my own skills
Erebus I've batswarmed (and possibly gotten a mass charm or bite in)
UB, I've spat
Rook, I'm probably behind my towers, possibly used a Boulder Roll
Sedna, I've already healed the damage and debuffs so Deep Freeze does no damage to me. Plus, I can just heal the "Silence" off of myself.
Well, if I've used those skills, then I'm on cooldown, which makes your Deep Freeze really not a Silence because I've done the stuff I plan on doing. I might need to wait a few more seconds before I can use my 7-second skills again, but meh, it really comes down to a 2 second Silence.
If you do Deep Freeze - Rain of Ice - Frost Nova (if they keep coming) then:
Sedna just heals
Anyone else just backs off for 7 second seconds by a tower if you get an Early Deep Freeze.
Now it's a proper "Silence" but if you make the Cold Aura deal damage then it's another hundred damage or so to worry about.