The only way their levels make any sense is if you get basicly no exp if someone is a lower level in your party. But then i wouldnt even be relevant whether he needs more exp or not for them catching up. In other words: these levels are just bs
Maybe she will kill everyone except for the last one and then loses and get memory loss for a few years and then have to kill new underlings before she can kill the main antagonist. Believe me its flawless writing