the mana usage on other builds isn't so bad. Spamming hammers costs up to ~30 mana per second, blizzard only ~25 mana per second. Of course, thats not counting tele/static/charge/etc.
but spamming freezing arrow can cost ~50-55+ mana per second. And at level 90, sorcs/pallys/zons have a base 213/162/162 mana. And pallys have both meditation and redemption to refill their mana, sorcs have warmth.
then theres the huge mana inefficiency. That sorc might hit a 50% CR target 3 times with one blizzard and deal 23k hp in damage for 49 mana = 472 damage per mana, while the zon might shoot FAs to deal a single shot of 800 hp in damage for 22 mana = 36 damage per mana. The zon can shoot 4.5x the rate of FA per blizzards, but the mana efficiency would mean using 13x the mana to kill each target compared to the sorc, on a zon who probably has half the mana to use between lower stats and no warmth.