I felt that Barthandalus was suppose to have the situation "under control". (SPOILER)He had been thinking out this plot for generations, overlooking the danger of trusting anyone to do his dirty work would've been a glaring oversight. Bart killed Jihl right away because he was probably aware of the unpredictability too much giving power to humans could cause (see Cid, who tried to kill the l'Cie to stop them from destroying Orphan). It's only in the final moments of the game, when Fang and Vanille use Ragnarok to save Cocoon's inhabitants, that Barthandalus miscalculates.