In those three months. Zetsu made them fight wild beasts to accumulate combat experience and put them through hell. Brink of death anytime. Of course, this was true for Kazuto and Kidd. However, Rozho and Shu didn't have much of a hard time. As for Caleb... Even a Tier 9 Apokalips of 2nd Variation might not be his opponent. What's more, a mere wild beast...
He was still a human, but his abilities had already exceeded what his race could do. Even the tests... They were too simple for him. He didn't even need to exert himself much. He only showed 34% of his strength, yet Zetsu and the others were already in awe of him.
