I fear that won't do.
a) That douche is a stereotypical highborn-noble-manga a**hat, that won't give up after his first beating.
b) Bro used his brother's own powers against him. That guy will still think of his brother being not powerful enough, needing to borrow strength to pull this kind of stunt and himself just being caught flatfooted this one time. Well, that is acctually what happened. (Though the noble brother shouldn't underestimate the half-noble brother's skill in tactics, which he will of course do. Yet, still that trick won't work for a second time.) Underdog brother should better come up with something to rival his brother fast and instill some respect into him, because this here won't do and his girlfriend is in real danger now.