I just dont see the problem, maybe thats because im actually playing cold sorc and not just speculating. Ignoring infinity as a balancing tool this actually wont effect hell farming at 24 skill points. All good builds scale well in the 30-40 pt skill levels. If blizzard was on left click i might play that to see how much better it is but i would assume its really not. if orb does .00001% of their health per cast blizzard wont be too gamebreaking. If blizzard was worried about balancing they would have removed one of the psynergies from blizzard and blessed hammer.
If it was intended, and is just a bug fix it still doesnt seem to be a problem. you still do no damage to cold immunes in chaos and baal runs. i havent tested every cold immune but those are the 2 most farmed end game areas with a group. i doubt youre going to be running pits for mf as a cold sorc without a good merc either.