Bah, I could take one. *makes shadow boxing moves*
They've got cool spells and abilities, but the problem is each round they use them, they're getting a good pounding. With enough buffs, he'd be dead before he got around to dispelling them all, so that's pretty much out. What would scare me the most is he'd probably use blasphemy as soon as you closed, which would hurt your ability to hurt him a little bit. Most of his mean tricks, like teleport, aren't really as effective in CRPG's, which tend to be toe-to-toe affairs.
Not to mention, Balors have been noted as being wimpy for their CR. Their celestial counterparts, solars, wipe the floor with them so bad it's not even funny but are only CR 19.