Agreed. Physically, the Ogre Mage isn't much stronger than a regular CR 3 Ogre. They'd be CR 4 at best, if it wasn't for the fact that giving a low CR critter a 9d6 cone of cold would be completely insane.
As for the "Master Manipulator" bit that refuses to go away, they can cast Charm Person and Polymorph once a day each. That's it. That isn't remotely enough to give the Ogre Mage some sort of massive "Social CR" bonus, unless every petty Sorc or Wiz is some sort of social god. (And don't get me started on the Bard. They'd have to be CR=levelx2 or something)
So no, I don't think the ability to try and sneak up on the party to cast a single, so-so 1st level spell that even the party fighter has around a 50/50 chance of saving against is enough to double it's CR. Nor is the ability to run away and live to suck another day. Ogre Mages are awesome at running away, that I'll admit. They make way better cowards than manipulators. It's just sort of pointless.
As for the "Master Manipulator" bit that refuses to go away, they can cast Charm Person and Polymorph once a day each. That's it. That isn't remotely enough to give the Ogre Mage some sort of massive "Social CR" bonus, unless every petty Sorc or Wiz is some sort of social god. (And don't get me started on the Bard. They'd have to be CR=levelx2 or something)
So no, I don't think the ability to try and sneak up on the party to cast a single, so-so 1st level spell that even the party fighter has around a 50/50 chance of saving against is enough to double it's CR. Nor is the ability to run away and live to suck another day. Ogre Mages are awesome at running away, that I'll admit. They make way better cowards than manipulators. It's just sort of pointless.