This is a good build, but either need to team with a Dopplesoelner, Monk C2, or Psychokino to fully utilize the Icewall shooting combo.
Runecaster is good, but it is a hybrid class, Wizard usually require a very specific target to pursue a specific goal, hence Runecaster doesn’t fit so well except for those who pursuing Icewall+PhysicPressure combo.
Another thing is, Hagalaz/Rune of Destruction should be Lightning element despite how it looks (and in reality it is represent Air element!), I think it could be fix in near future. If it fixed, it could works very well with Hail + Rain.
And in future, we doesn’t know what is Rank 8 yet, but it is very likely Sage is 1 of them, i’m not sure are they will doing the same thing like in RO, which is to enchant element into your normal attack. If they are able to enchant Ice Property or +Property damage like Pyro, which could mean Runecaster + Sage is a very solid combo. (They are wearing Robe! and it hint that it could be a support class.)
@Ziroth
As many said, Isa does not support “deployment skill” which mean Hail and Frost Cloud are not supported, only Freezing Sphere is.