I understand what you mean, but I think that might depends on the actual game needs to. For instance I think in the game I am trying to design, it would actually be more maintenance if I had to manage a list of spells per character. Whereas by having a Magician class key on each Spell, I can set it to be available for Magician, Merlin or Gandalf. In other words, shared by all magicians or specific to one.