Leia in Heroes vs Villains...You can get mauled fast there, as most of the maps are made for close encounters. The shield won't help you against the lightsabers, so you will die a lot. Leia is pretty good into countering blaster heroes and Palpatine, but she is done if Maul, Ren or Vader are near. And those three can cover the distance fast (don't forget that the lightsaber heroes can jump higher and further than the blaster heroes). Even with the blind grenades and lots of dodging you won't get away when a lightsaber hero is near Leia. Couple of slashes, later she's down.
Yes, Leia is good in really specific situations, but most of the times she is in the middle or dead last.