Gonna have to disagree, least in part. MC could have very easily disabled the antagonists without killing him. Interrogation would still be possible and the villian wouldn't have a chance to resist further.
While true letting them monologue while they still feel a mesure of control is one method of gaining information, it is by no means a guarantee. This scenario also allows the enemy to much freedom to act. They can practically do anything from casting spells to attempts at escape.
So just knocking them out of their vilianous actions doesn't remove their ability to act. It only makes them more cautious and unpredictable. Much better to fully restrain them, or otherwise remove their ability to act. Questions can come after the situation is under control.