I have seen less of Kennen than any other Dominion champion. I have seen more people try to make Tryn or Galio work than Kennen. Energy based champions are in a poor spot on Dominion, unless you have an OP kit like Lee Sin. CDR is the best stat on Dominion, but energy champions get very little benefit from it. Runes to help with energy are horribly overpriced and overspecialized (how many people own energy runes, aside from that one person obsessed with Kennen? Probably in the single digits.), and there are no items to improve it either. Mana mages have access to cost effective items to help them like FH, chalice, or even just a simple pro ring. Kennen can't use any of these to help him. Shen's in a pretty similar boat, as being locked out of FH really, really sucks for a tank.