Hailstorm was never meant for solo play. As in matter of fact, Mage is never meant to be solo play. Neither are the other classes are meant to be solo play. Harder dungeons like Peaca favors a party of players who have variety in their skillsets and etc.. Hailstorm is meant to be used in certain places where it excels, and then there are places that it should not be used where it does not excel. Since this skill locks you into place, it wouldn't be wise to use this skill on, say Cave Dragon in Raid, because Cave Dragon will most likely flinch you before you can get past the cast time and the charge time. Hailstorm should be used when you know that you are secure enough to cast it without you getting flinched from any nearby mobs. This is why Barrier Spikes users are so valuable to Mages because it can block about 80% of the threats Mages have when they are unable to move.
To be honest, I wished we also got the 40 second buff that Live Hailstorm got as well because the 30 seconds on Pro's Hailstorm includes the cast time for the skill, essentially only giving you 20 seconds to do damage. If we got the 40 second buff, we would have true 30 seconds to do damage. I feel like if we also got the 40 second buff the skill will outweigh the negatives by a huge margin.
The time increase would be a very welcomed thing, however there is little content that can handle the dmg, if done right, outside of very end game bosses, for those extra 10 seconds. Still would be nice! A counter would also be great if possible.
It is true that you can't really solo with hail, and it's meant to be used in particular situations, but not many situations call for the spell outside of end game or near end game content to begin with, making it...very lackluster until rank 1 (like most magic). It suffers much harder than any other magic skill, only equal to fireball in this, in its cast time and locking you in place. IS, TH, Fusion bolts and basic bolts, and even blaze, all are much faster skills, MUCH faster really. So standing still for 6.5 seconds just to get your FIRST charge, hitting 10.5 seconds - 9.3 seconds depending on rank, just to hit the full charge. (I might be off on that math). Many other skills are faster than magic and, in most content, get the job done the same way. Not all content mind you, but a large chunk of it.