"Power is only valuable if it can be harnessed." [Mythos][3.5/PF]

[noob]

A quite hard thing is that casting a ninth level spells needs a total of 198 magika(9 essentia stored in the spell and spending 153 magika on casting)
So you need a total boost of 98 magika from the initial pool to cast a ninth level spell.
You get roughly 40 bonus from level ups at level 20.
You then need to obtain 58 magica from other sources.
You could get 3 magika from the three bonus feats excellency then with a con score of 20 you would need to take 11 times the extra essentia excellency.(With 30 con you drop to 6 times)
So casting a single ninth level spell more or less spends the resources of an entire day(you can not have other prepared spells or else you no longer have enough magika for casting the ninth level spell) and just having it prepared take 45 of your magika which is a huge cost in itself.

So this class is so bad at casting high level spells even a 5E wizard is better at that.