There's also the fact that among Grey's first experiences was being rescued by a stranger. In essence he was given a crash course in benevolence before he came into contact with Model A. Perhaps if PnP had attempted to take Grey as a pupil, or even if Grey had found Model A while on the run, things would have been different.
Seems to be a recurring point of interest what effect, if any at all, the mind control has on the host. Thetis always has me raising eyebrows on that one. While the others seem to fight for pain, vengeance, and superiority, Thetis has a noble enough cause. He's just going about it the wrong way.
Then there's Giro, back in Z1. Model Z was obviously being suppressed during the battle with him, otherwise he could have canceled the transformation of his own accord. I wonder, is that incident related to what was done to Grey and the four? Does Model Z's status as the only Biometal to come out of such suppression (after sound beating) have anything to do with his last-ditch effort against the four in ZXA?
Man, the speculation can run pretty rampant there....