Although Arnold and Swain don't seem to get along very well, they actually cooperate frequently. It's just that Arnold doesn't like Swain's cautious style.
Even though he says he doesn't like acting with Swain, Arnold is well aware that a person like him actually needs someone like Swain to clean up his messes.
Swain is always able to take into account situations that Arnold hasn't considered, and Arnold just needs to charge forward and defeat the enemy, leaving the rest for Swain to handle.
As for the Tenth Legion, it was quite normal, since Adric and Swain have a mentor and friend relationship, and the two legions have always had a good relationship.
After Lucas sent Duke to the deserted island, he politely declined Duke's invitation to come up for a cup of tea, saying, "I have things to take care of. Don't leave Black Sail for the time being. There might be more things to ask you later. Also, apart from us from the Third Legion, you can ignore other people seeking you out."
