Whoa whoa whoa, Superman Deathstroke is NOT 7-3 in Superman's favor. I've played 40 sets a few days ago with a competent Superman player, and he actually believed it to be in Deathstroke's favor. Deathstroke's air control and ground control makes it so Superman is forced to play Deathstroke's game, which is chasing Deathstroke. This is good, this sets up your opportunities. Your best friend in this match up is j.3. This beats all of Superman's jump ins, his f23 if you predict it's coming, and sets up your pressure game, and it also beats his Anti Air Grab on the start up. The only thing Superman has on you is his ability to poke, and his range on his normals.
Now at the start of the round Super man has a few options:
f23 (Which most do) -This gets beat out by Jump back 3 or jump forward 3
back dash- Which nothing happens if you do jump back 3, or you follow him for jump forward 3
Superman punch- This beats all your jump options, so just block
jump- Which would get beat by jump back 3 or forward 3
Now I can understand why people why say it's a bad match up, but here's a best friend you can use. PUSH. A BLOCKU. Let's say he gets in and starts doing f23~Ice breath (Which you can check with d1~Sword flip if you know he's gonna do the string twice or three times.) Push block him away and now he's not in range to do f23 anymore, he has to guess between dashing in, jumping, or walking forward. Which if you react properly, can score you a knock down from far away, or set up your pressure game. Any time you have the opportunity if you can spare the meter, push him the fuck away. You play Deathstroke to annoy the other player, so do so.
React to his air lasers, you can literally just react to it, but keep your guns going. I.E, shoot quick fire or low guns full screen to make him respect your ability to zone, and when he jumps, shoot him out the air. If he gets you into the corner, it IS NOT OVER. This is where learning how to block comes in. Superman has an okay high low game from certain strings, and I've always said that block low before high against Superman. Meaning react to the high and just block low. Also react to throws. Lastly, ABUSE J.3 A LOT.