I believe Blizzard was changed for 1 of 2 reasons. PvP, or FATE's. When I leveled my BLM (my first class I FATE grinded with) I saw so many people complaining about me and the other BLM being able to tag everything with such ease and no loss to MP (yet no-one complained about Arcanist and such spamming Flash. xD). Lowering the damage so much makes it almost useless to use on your own, as Freeze used to be. However, if 20 people in a FATE are spamming it? 50 Potency is much better than 100 in this instance.
I can't really think of a situation where Blizz II would have been overused in PvP. You have to get close to be able to use it, and being close to someone usually results in you not being able to do anything. Binding someone who's right next to you seems useless unless you predict them running away before you Swiftcast Flare.
Blizz II wasn't really a huge part of any rotation, either. People have claimed it was nerfed because it was part of some huge DPS Flare rotation, but removing this from that rotation would barely affect the DPS. I strongly believe it was meant to balance FATE's, since now all DoM classes have Blizz II while everyone has Flash. I'd rather 50% spammed Blizz II than 100% spammed Flash and nothing got done. Though, I honestly couldn't care. The only times I used Blizz II was against Tonberry on last boss of WP, but now I just use Flare or Freeze.
