You might as well have killed him there Crest, if you really want to be better than him, letting him have that kind of fate despite knowing what they will do is far worse than just killing him.
Of course if MC wanted to get revenge then I would not say anything about his action, but with what he just say about being the better person, frankly, his action just now is extremely contradictory. Because while he may not have personally killed him, he gave the guy a far crueler end.