ToME: the Tales of Maj'Eyal

I'm playing an archmage, and I decided to play full storm. I had the first 30 levels already planned, lots of theorycrafting. I would be able to defeat urkis and the daikara no problem as long as I grinded to level 22 to get tempest and a few other items to pierce through lightning resistance. But the I try to get my sher'tul fortress, because I like to get that ASAP and... I just can't.

I got through the sad water level, and then I face the weirdling beast and it just ends in a stalemate. It doesn't even have 100% lightning resistance. It just gets massive shields, and gets rid of all my sustained abilities, so I have much weaker shields, and then I don't do enough damage. I run out of shields before I have to retreat. And well... it hasn't kill me, because I have a lot of defenses, but I can't kill it either.
I did another run, more offensive, went for urkis at lvl 12 and was fine, just so I had a bit more strenght before the shertul fortress, and I still couldn't defeat it.
I could probably grind more before it, but the problem is that I like to get like 8 sustained abilities, and this thing immediately gets rid of 6 at the first contact, and to add insult to injury it gets rid of my last 2 a couple of turns later.
I feel like if I go full damage, and no sustained abilities I'll just die in the daikara.

Is full storm mage just not a viable strategy?
I'm doing it for fun, not trying to min-max or anything tryhard, but still... I'm shocked that it doesn't even seem possible.

Since you killed Urkis you should get back to Angolwen and claim your reward. The rune of dissipation will remove Weirdling Beast sustains, making him a much easier fight.

You can also just come back later :p Weirdling Beast is a level 20-25 fight at the earliest, dunno how high level you are right now ?

Full Storm Archmage is perfectly viable and possible though i'd advise to still put points in the good talents of other trees, like disruption shield, entomb, etc... even if you go with a main focus on lightning

Wow, I'm so happy my theory crafting was in the right direction, I did decide to go for disruption shield. I guess I'm just way too used to fighting the weirdling beast at lvl 15(with lots of time), but I think the run is salvageable if I just accept I won't have access to my vault until much later. I don't have anything that's too synergistic with storm mage anyway, as I already got some gloves with lightning resistance penetration.