I don't know about that, since Sarevok knows more about Bhaalspawn then anybody. That's probably the incentive to recruit him, for his vast knowledge on what you're capable of.
As I said in another thread, I think by the end of SoA at least, your own knowledge would be more extensive than the game seems to give you credit for, especially if you're playing a mage or any other smart, scholarly character.
Also, I think you have every reason to be at least somewhat dubious about anything he tells you, unless bringing him back to life with your own power binds him to you in some way, like a geas. He is, after all, an arrogant, power-hungry, backstabbing Chaotic Evil bastard whom I wouldn't trust as far as a one-armed halfling child could throw him.
And to me his glowing eyes signify that he's always been tapping into his Bhaal abilities ...
True, Tamoko mentions that in BG1 when she pleads with the PC to try and talk Sarevok out of his mad plans.
Speaking of the eyes, I wonder if he could "turn them off" -- going about his daily business of the normal, faithful son of Reiltar and a would-be Grand Duke of Baldur's Gate would have been kinda difficult with two baleful miniature flashlights in his face.
... but is more subtle and controlled ...
Hmm. My impression of Sarevok is the complete opposite: that of a ball of pent-up dark emotions which he can barely control, and only with reluctance. Sure, he was a schemer when he had to be, but even then, he seemed quick to lose his temper. I find it very fitting that he embodied Wrath in the Nine Hells -- raving, unbridled emotion.
... then the PC who turns into the mighty but reckless Slayer.
But only after having her soul, and thus most of her strength of will and other important bits, ripped out by a vengeance-crazed ex-elf.
Seeing that even Imoen managed to get her soul back (with you help) and that you yourself became even more powerful after the loss of your soul (Slayer change) I would not want to be Irenicus should he had attempted to get Sarevok instead ...
Fighters fare rather badly against high-level mages, though. I know Sarevok butchered Gorion, but for all that the games call our dear foster father a "powerful mage", the actual battle between the two had to make him look pretty pathetic, else there likely wouldn't even have been a BG1.
Back on topic: maybe you misunderstood me, my original musing was not so much about personal power, but rather self-control and strength of will. If a Bhaalspawn lacks that, and the sense to know that the divine fire in her veins is dangerous not only to others but also to herself, I think she'll lose herself to it, lose her will to the Father's, and become nothing more than a "weapon of Murder" as Sarevok calls it. An appropriate term, if you ask me, since a weapon has no will of its own, no control over who swings it, and at which target.
Sarevok may have been close to that state when you first killed him, at least that's what Tamoko thought.
Sticking to the fire analogy, Sarevok is a pyromaniac who doesn't care about the danger he's putting himself in when he fans the flames higher and higher, while the PC is someone who keeps a careful eye on the fire and finds other, less destructive uses for it.
(and that's assuming he could even get his hands on him, seeing that Sarevok would probably be much more difficult to kidnap then the PC, giving his paranoia and background).
He has one big weakness: arrogance. The possibility of failure or of being wrong never seems to enter his mind, and he does not really take opposition seriously. Same with Irenicus, though the two are otherwise totally different, IMO, excepting their hunger of power. Well, those are Required Villain Attributes, I suppose.

"Beware of the blindness of those who would follow, and the damnable lure of those who would lead."
- Tamoko
"Mmm? What's this? You gots hammer? Bhaal once drop hammer on big godly toe. Jump around and swear for days, he did. Kicked poor me all the way to Baator. Very bad week, that."
- Cespenar the imp