I'd rather limit the ruler's power. Better to encourage him to empower himself by giving others (allies) power positions than by hoarding them.
Most realms already do that. In the realms that don't have such rules, it would be highly frowned upon for a ruler to do so. Rare are the places you can pull it off, imo.
At least for the traditional dukes. If the ruler creates a duchy out of a poor townslands and makes himself duke of a one-region duchy, is it really that bad? I wouldn't think so, but I think that's something we can let the characters of the realm decide.
