offhand skills don't cost energy, regardless of how much damage it does, it's "free damage". Isn't it insta-cast too? Even if it wasn't, there's plenty of time between iceshards/iceblast rotation to cast it so I don't know really know why you say it's not worth casting at.
Yea it's not. And it's not also an "insta cast" since if u in rush to boss like snorri or sreng riding a mount, u need to equip it on ur hotbar and it will start its damn slow cooling down first bfore mage can cast it. And killing snorri or sreng only takes about 8 minutes max with 5 to 8 ppl. So the mage probably can only cast it once or twice at the end of its 1 to 5% health. Which iceshards with more damage could be casted many more than that (very fast cooling down compare to that offhand). Not to mention when u arrived at snorri or sreng with the adds following u behind and when u were on the effort to equip ur weapon and put that offhand skill on the hotbar, (2 different actions, first> menu-inventory-wep-offhand, then second> Menu-skill-scroll down to the bottom to find the skill (lucky if u can put it on the ur first layer hotbar, i doubt it for mage) or click the second layer of hotbar-drag it to the free slot-finish-and u found urself dead killed by the adds
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. After u rez, u still cant use this "insta cast" waiting for the cooling down. By the time it's ready, snorri or sreng only left 15% or 20% of its health lol. So u tell me if its worth or not to use it for making some damage. It's only helps to boost the stat. But not on damage. Just my humble opinion thou.