First of all, everyone should be able to cast spells, or they’d flock to another game. this is game design 101, especially for an MMORPG. Stop feeling special just because you spent 70 hours trying to learn wonky controls. https://en.wikipedia.org/wiki/Bushnell’s_Law
Secondly, i’m going to steal @seb_D 's videos for my Z-axis argument:
https://www.youtube.com/watch?v=75P3cym64W0 vs https://www.youtube.com/watch?v=gf2ah0DTC64
In the first video he draws perfect ice lances back to back, the second video he does the same thing, the rune looks exactly the same (from the front), but the camera angle is different, therefore the Z-axis is interfering, and boom: inconsistent. The exact same rune in the second video does NOT cast ANY spells for at least 5 attempts in a row. Flattening the rune before cast should resolve this. Consistency is the key word here.
Again, to repeat what i said earlier, runecasting should be easy to learn, but hard to master.
easy to learn = not taking 70 hours to actually cast pushback 2, but more like 1 hour tops.
hard to master = remembering to use it at the right time, drawing it quickly without making a mess of your rune, and practicing to get perfect casts off (not struggling for normal casts).