Kerb was completely unhelpful and mechanical when Rand was questioning him - and it was about this behavior that Rand was talking about. Kerb had no personality - he was completely replaced with whatever Graendal wanted him to be. Which is not the same as saying that he is an automaton, or a robot.

Kerb had initiative. He worked with the dungeons for several months - out of Graendal's direct command. He killed the messenger. He poisoned Millisair (though I understand it is your opinion that he was ordered by Graendal, of which I am debating ). He tried to escape when he suspected he would be caught by Nyneave. He apparently ate, went to the bathroom, and slept, and chose how to use and manage his time while he went about existing. His personality may have been destroyed, leaving him a shell following programing written by Graendal, but that programming obviously allowed for his brain to come up with creative solutions to problems he encountered and act on those solutions. From mundane things such as how to treat his coworkers, to (possibly) whether to kill the messenger. While it is possible that Graendal traveled to Bandar Eban to give him these orders, I find it very doubtful she would do so every single time.

I understand that you find it difficult to believe that Kerb could have chosen to poison Millisair or to kill the messenger. It just sounds like we have different opinions about what compulsion is and isn't able to do . My personal opinion is that it is very possible that Kerb made those decisions on his own. Especially if his orders were "Hide among the staff in Bandar Eban, and discreetly eliminate anyone who may compromise my security. If you are suspected, reveal nothing."

I always conceived of compulsion similar to brainwashing - at which Graendal was the best. She was skilled enough to make her own "Manchurian Candidate" an assassin, so brainwashed that he couldn't control what he was doing, but who decisively used all of the creativity and judgment of the human mind to execute his objective(as a matter of fact, the more I recall about the film (the 1962 version, that is) the more similarities I see between Kerb and Raymond Shaw). RJ grew up during this era too, so it probably isn't too much of a stretch to suggest that some of those ideas about mind control and brainwashing made its way into his writing.

Regardless, I don't really think that this is a subject we can come to a conclusion on. Your opinion is that Kerb's compulsion couldn't have allowed him a very great degree of freedom, therefore, Graendal had to have been directly involved. My opinion is that Kerb's compulsion allowed him to make decisions, without Graendal's direct involvement, and his actions led Rand to Natrin's Barrow. The truth is, we don't really know that much about compulsion. We heard a few hazy stories - daughters convincing their fathers to accept bad boyfriends, Verin puzzling out her own version, and suspicious behavior by a few characters such as Noal.

*shrugs*

As it is, I can understand why you think the buildup to Graendal's death was odd - Kerb's behavior is odd, and defined by his compulsion. And we don't really understand how compulsion works.