Alright... last time I answer this cuz I already explained, but I'll go into a little more detail this time. Your not trying to trade IAF with Kitana or Kabal cuz they win that trade. When they do IAF, you do low fireball, they land on the low fire and they get knocked down, after they get knocked down that's when you start your IAF's. Assuming the Liu Kang player is good @ doing his IAF's, that will leave Kabal or Kitana no choice but to come in. If Kabal or Kitana try to do their IAF after Liu starts his IAF, they both lose. If Kabal tries to throws saw blades, Liu gets 1 guaranteed IAF fireball and 1 blocked IAF 1 and the saw blades don't hit Liu cuz he goes right over them. I've played some of the best Kabal's and Kitana's and they don't ever out zone me cuz they can't, they win by rushing and Liu has frame traps also.
Edit: Lui Kang blows up some of the best zoners in the game when it comes to fireball wars, but doesn't get a whole lot off his fireballs, they just keep you in check. The reason I think he's the 2nd best zoner is because, he out zones some of the most dangerous zoners and zones well against the not so aggressive zoners and rush characters.