Been working with a spell-based cultivator a bit. True Sun cultivator, boar Yaoguai with pretty mediocre stats all in all. Took as many spell power manuals and actual spells as I could: Innate Qi, Firestorm, Divine Bolt, Chaos Void, Vitality Chant, Reversa Cycle, and Spirit Shield. Tried to max out Spell, but only got Protect to 10. Equipped a Giant Turtle Shell, Flood Dragon Scale, and Taiyi Codex, ate a Shield Pill, and she's wearing Demon Hide clothing. Artifact is weak, total power 651 with 7k qi capacity.
She blew through 3 attainment tribulations pretty quickly with little difficulty. She probably could last almost indefinitely, especially if I get some bonuses to cooldown. One tribulation was difficult for my Grand Chariot and 7SS guys. But that's probably because tribulations have no protection value; they take full damage from everything. Against a PS-level cultivator with 60k qi but 20 Protect, Firestorm, stated to do over 128k qi damage, did less than a tenth of that and has a long cooldown. On the other hand, my best Grand Chariot fighter killed that enemy and his two buddies within seconds.
One thing I also discovered, Heaven's Breath, though very difficult to acquire, makes awesome artifacts. It's naturally T12, so you just need a really good Myriad Artifact Law user and to set the item in a qi array until it have at least 1500 qi.