Laz had no intention of using his full abilities even though Aaron was clearly a late stage foundation realm. This wasn't due to him being arrogant but because he didn't want to do something he might regret. If it was a small and narrow use of his black flame energy, Laz felt that he had perfect control over it. If he didn't he would have never had been able to help out Sarah or Abraham. But once you unleash the beast in an attack, it was hard to take it back.
Unfortunately for Laz, trying to use physical abilities to deal with Aaron was impossible. It was like trying to catch a shadow with your bare hands.
It couldn't happen.
But luckily for Laz, he wasn't out of options.
