@traveling_chef This is a re-telling of the story. Checking MangaUpdates/NovelUpdates, the author and artist are the same. Meaning, the change was a preference after considering the original story. So neither arbitrary nor pointless. If it was, the entire story would be arbitrary and pointless, since it came from the same creators.
Also, the characters were not useless. They served to expose Lock's intent to help groom young adventurers, thus giving better character motivation than
"I killed the Big Bad already, so I guess I'll start over ¯\_(ツ)_/¯"
But everyone is free to their opinion.😊