I have to go with Myenshi on this one. Ezra indicated that Thrawn was the one who discovered the Nightsister temple & forged an alliance. Clearly he wouldn't have done so if the circumstances didn't warrant it. As I've theorized previously, I still think his reliance on magic witches is a result of his own forces being severely depleted, and this last episode did nothing to disprove that theory. And I can't think of
any other Imperial admiral in the SW canon who's ever displayed the acumen to
recognize the need for outside assistance let alone act on it, so on my Imperial Command scorecard Thrawn's already way ahead on points.