Just ask the PC players, they had this kingdom 5 weeks ago.
Great Maw on your team is literally the only good pick, but the entire team strategy is a failure from the start because by definition if you can’t cast spells (more than once) then your ONLY method of winning is waiting for the stars skulls to align in your favor. Good luck with that.
One-shot spells are pretty rare, and most of them are indeed associated with Drifting Sands. It’s just not something you can build an entire team around.
The good news is that the devs HAVE tweaked a few Trials (Stormheim and Grosh-Nak), so at least some feedback is getting through. The bad news, of course, is that’s only 2 of 37 Kingdoms (counting Vulpacea).
The best trial so far is Adana because you have P4-NTH4 on your side, which scales by enemy Armor (making it an almost guaranteed kill at high levels).