Cole received the highest talent grading that the crystal could possibly test, meaning that his potential could still be higher than that and it was still yet to be tested.
Angela was still not mentally strong enough to be a great cultivator and yet had received such great results, and he also felt that there was more to her Water Elemental Affinity, so she still had a lot of space to develop.
Chase had never had his talent grading tested, but had great cultivation speed and perceptivity, along with a very durable body and Unique Skill. Along with that, he had the Monk Inheritance and was a battle and training fanatic, making him a perfect fit for being a cultivator.
Elizabeth had her special constitution that she was yet to fully explore and there was still so much that she hadn't experienced or learnt about that would greatly increase her capabilities.