Regarding Deathstroke...he isn't winning tounys because he zones, he is winning because once they get around his zoning he has a stupidly good close range game to put them back fullscreen.
Thats his game though. He does his little 20% combo and pushes you full screen to do another 15% in chip as you come in. It's extremely frustrating and that is the point, but if you are patient and just stomach the chip damage to get in again, your fine.
Deathstroke's offense up close revolves around knocking you back again, but this isn't even close to what happens if he gets knocked down by someone like Doomsday or Nightwing or even Bane. He enters a mini vortex where he has to be scared of another mixup as he wakes up and has to hope for another opening for his baby damage combos to push the rusher back so he could get another 10% in chip again lol.
For GL, Superman, and Black Adam. Their projectiles are basically to force you to do something and force you into the range where they want you. Again though, realize where they want you (mid distance is the answer for all three) and predict what they will do and counter it. Like neutral jump from mid distance if you predict a Superman F23. These three characters use their projectiles more like Ryu from SSF4. He doesn't really zone, but just forces you into positions where he wants you with them.