When it comes to spell interpretation, they're practically scraping the bottom of the barrel.
It's not that their spells are bad, in fact, they're sort of okay when put into use, like Xie Shuling's attack spells are pretty awesome.
But spell interpretation is the foundation of cultivation, cultivating the future of disciples. Just because you're good at fighting doesn't mean your cultivation will go smoothly. After all, even if you're a sword or blade cultivator specializing in combat, eventually, you have to face tribulations and discuss the Dao, right?
This is Wuque's insistence.
Poor Xie Shuling.
Those awesome attributes of her spells were perfected through countless PKs—epiphanies in the heat of battle.
It's not entirely accurate to say she has low talent. On the contrary, she has quite high talent.
But asking her to articulate the rationale, to analyze the origin of Dao and spells, she's completely clueless.