While strong, I don't think Tainted Sorcerer or Tainted Scholar are as strong as people think at first glance. This is because you can't use their metamagic abilities to enhance a spell beyond the level you are capable of casting.
I'm not saying they aren't strong, they are, but when you can do things like the Incantatrix or Anima Mage, it's not that big of a deal. An Anima Mage effectively has infinite uses of his Vestige Metamagic by level 10 when Persistent Unfettered Heroism comes on board.