Finally, Neo's phobia can come into use.

Classes just seem to be a good way of defining certain aspects of characters. Grandmaster? Understands battle tactics and sees the flow of a fight very well. Beserker? Every blow should cleave a stone, or enemies helm covered head, in two. I would assume Snipers can shoot farther than Archers and Sages are magic users who finally decided to delve into other types of magicks.

As for HOW actual promotions happen, my own theory was that either a Lord or Tactician would "knight" a player for doing a certain grand act that could have been the starting point of a new role/class. Even something as simple as an archer stealing an enemy cavalier's horse and taking the steed and sword as their own could almost pass as a promotion to Bow Knight. Again, in my opinion.