It seems to me, if any given class were significantly overpowered, that class would be targeted much more often by any intelligent enemy. So it seems to me "unbalanced" would be self-regulating, at least over the long-haul.
That said, I might let the "Charm Person" on the chamberlain succeed. But how precisely would you get the chamberlain in a position where he is unguarded and you're allowed to cast spells upon his person? That would be the actual challenge, more so than beating his Will save (though it would probably be solid).
That and, once you've charmed your way in, not getting killed for the insolence of it. If not by the royal guards, then by a loyalist serving wench, with a friend who's an herbalist, at your victory celebration.
"My favorite character class is super powered and everyone else's is lame" sounds to me like "the DM lets me win by having my enemies be ninnies who fall for all my plans, never come up with their own, and never recognize I'm a threat they need to eliminate".
Tennis with the net down, as it were.