Often true, but beware generalized statements. Depending on the individual's original nature, the strength of the tempering, the amount of times tempered, etc., mindless berserkers aren't uncommon, either. We have examples of tempered who are pretty much themselves but have "found God" and cannot be convinced otherwise. We have examples of more or less normal, functioning people acting as sleeper agents because of their unshakeable belief in the primal. We have seen people who just yell "FOR THE LORD OF WHATEVER" and go to battle against hopeless odds.
Complexity of their usefulness varies, it's their obedience that's absolute. What active orders they've been given "for God" plays a lot into it.
Side Notes...
Ga Bu
I think Ga Bu being (SEEMINGLY) lightly tempered for a short time by a primal that was party in his own image and gave him no active orders is going is about as optimistic as we can get, but we'll have to see. Maybe that's our gateway to more reliable information.
Lakshmi
Agreed. Not inherently evil. She seems to be the result of a paradox, to me. Primals that are summoned to be gods think that they are true gods. The Qalyana asked God for deliverance from something that they themselves believed was hopeless. Lakshmi is the result, offering them an escape into a blissful dream ... "Salvation". In turn, she sees your rejection as paradoxical, and when only "The Saved" provide crystals, if she can't manipulate people into accepting salvation, she gets angry.
Susano
Susano seems like one of those primals that's not thought of in a way that's conducive to spreading and tempering and conquering and defeating adversaries. He's just a jolly old false-kami that revels in all sorts of things. Granted, he'll still drain the land of aether and eventually aura-temper those around him, so he had to be put down, but otherwise on the lower end of the primal threat tier.