a neglected gripe against Khans is how these cards are not only 3-color monstrosities, but they're also midrange as fuck
That's almost unavoidable though. They can't cost less than 3 and you can't expect an aggro deck to always have three colors on turn 3, so really you can only make an aggro card a 4 drop. Not a lot of design space with those constraints.
Tri-color sets can't help but suck due to the inherently restrictive casting cost.
EDIT: Although I guess you could do hybrids or toss stuff as activated costs, etc. I'm being a little myopic about it I suppose, but I think the color restriction is a problem anyway you slice it.