I don't think Malak was Revan's apprentice during the Mandolorian Wars.
I remember that on a KotOR splash loading screen, it said something about Revan being stronger of the two, and
Malak reluctantly assuming the role of apprentice.
This sounds more like, they started off as friends about the same age, and once they took on the ways of the sith,
one of them had to be the master and the other had to be the apprentice, and the master would be the stronger one, which would be Revan.