And he sounded pathetic because those words were hollow. Sometimes you've got to admit you were bested. Plus he didn't say he was weak, he said it wasn't his destiny to rule the galaxy.
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.