Semantics
How long had it been since he had access to Tier 4 of his Ability Index?
Leonel only had a very vague understanding of Abilities when he began his journey. However, by the time he had been able to comprehend, he had already entered Tier 4. It could be said that from the very beginning, he had always been in such a state.
What did that mean? It meant that since the very moment Leonel had awakened his Ability, he had gained with it a perfect sort of control over his body that extended to his mind. This sounded like a great thing, but when he was completely ignorant to what he was doing, he was essentially digging himself into a larger and larger hole every time.
Whenever Leonel believed that he was able to easily cut off his emotions because that was just the kind of person he was, naively believing that this would have no impact on him since he could so naturally do it, the reality of it all was that this was just an example of his Ability at work.