I really don't get all the Spartan III speculation, because these are definitely not the Spartan III's we've read about in Ghosts of Onyx. Regardless, the original batch of Spartan III's didn't work together as a cohesive unit as well as the Spartan II's. They weren't "fucked in the head". And the second batch, were given a new augmentation which in times of extreme stress, allowed for the more animalistic part of the brain to take over to hone their reflexes, reaction-times, etc, instead of the human part which gets sloppy with emotions, pain, stuff like that. But they weren't "fucked in the head".
And yes, they were pulled from a pool of survivors from fallen colonies, but still at a very young age, just like the Spartan II's were. Technically, they received BETTER training than the Spartan II's did in some aspects. Mendez was able to hone his program that he uses on the Spartan II's, and they had an actual Spartan II training them.