The point I was mostly getting at was that I felt that more base classes should have access to Disguise as a class skill. I can think of a good reason for Sorcerers to, for instance, since they are not well regarded around the Core and many would actively either disguise themselves to be avoid being ousted for witchcraft, or, in the case of Dementlieu, not being a wizard. Since they have access to influence, which isn't one of their PnP 3e skills, I don't see why we can't indulge PotM Sorcerers Disguise.
As for other classes, I can easily see it befitting Wizards for a similar reason as Sorcerers, though to a lesser degree. Additionally, Druid, since many Druids do shapechange to conceal their identity. Beyond these three classes, I could maybe see a similar argument for Hexblade being made but I'm more harder pressed to explain a Fighter or Barbarian's inclination towards the skill (nor would any build for these likely have the skill points to invest into the skill).