She may not be the greatest Legendary Creature to build around. But, she's certainly pretty good in a deck that utilizes tap and untap shenanigans like the Evasive Maneuvers deck that she comes in. Beyond being Mind Control on a stick, she's just a 2/3 for 2GWU, which is okay. She's nothing special, honestly. But in the right deck, she's very solid and can cause a lot of issues when she's able to tap and untap at will.
True, there are cards in White, Blue, and even Green that pretty much do what she does. But she's a classic Legendary creature, and some Derevi, Empyrial Tactician and Roon of the Hidden Realm players have kept her in the deck she came in. But she's hardly ever going to be popular as a Commander. Still, Bant is a great color combination to build a Commander deck around. So, as a relatively non-threatening Commander, you can build a sneaky good deck around her.