The legitimate answer to your question(s) is that they are useful at low level/while leveling.
Blizzard II is more potency than Blizzard I on four targets after you've used Transpose and are waiting to Transpose back into Astral. After you learn Fire III, it becomes mostly useless (particularly now that Thunder II is aoe). It also has a really fast cast, so if you're in a situation like fate grinding where mobs die really fast and you can't get fire casts off, spamming Blizzard II is a legitimate strategy.
Sleep can be very useful low level for recovery, if your tank dies you can sleep the mobs etc. Freeze is the same way. These become mostly useless after the 2.x level 50 dungeons where most mobs resist most status disorders like this.
Scathe is marginally useful for movement, but I also use it as an "execute" when the last mob has low enough HP that another full cast will not complete on it.
If it were up to me, Scathe would be buffed to become useful but the other skills can pretty much just stay the way they are. Not all skills need to be useful at max level, in my opinion.
What I might do is have Blizzard II upgrade to Freeze and have Freeze be some kind of off GCD spell that hits every target that has Thunder applied to it for some amount of potency in ice, sorta like Fester/Painflare.
