Yeah Malak admitted his defeat that's ok, but I don't like him for saying "You did every thing, I just stole your power, I am nothing." As a Sith he should vow for revenge, as the Sith apprentice of Revan he should believe he would surpass his master.
Why would he vow revenge? They both knew it would be an empty threat. Revan defeated him and he realized he had failed in the end to take Revan's spot. He probably realized it was pointless to swear revenge he could never carry out as he was dying and used his last breath on something else. He didn't exactly say "You did everything, I just stole your power" either.