Gateway mids I thought were covered really well with the Warrior/Scout/Element. The Karma and Warrior kinda overlap and and the Mystic and Element kinda overlap IMO; the Scout kinda sits in the middle of it all. Once you try to work the Scout in, you will either a) will decide you don't really need it and can cycle either a Warrior or Karma into that slot or b) will decide it fits nicely in-between a Warrior/Karma and a Mystic/Element and will want to carry it. At any rate, you basically can't bag all five without massive overlap. You really have to throw them and see what combination of two or three of them works best for you. When I throw Gateway mids I still just rock the Warrior and Element personally. I have a buddy that uses heavy Scouts like I use Warriors becasue he hates beaded discs. To each their own.
If course I'm leaving out the Demon as it is its own beefy sort of category. They also call the Blaze a mid now, but I don't buy it. If the Blaze is a mid a Banshee is a mid...just sayin'.