Superman is at best a 6/4, but probably 7/3, in Superman's favor, based on the following reasons:
1. Once Superman gets you in the corner (and he will get you in the corner), Deathstroke's only options are to eat a full combo and pray that Sword Spin comes out as a wakeup, or he can pushbock. Let's examine those options:
If you do manage to get Sword Spin to come out as a wakeup and Superman continues to bulldoze you with f23, you can spend 2 meter to get a 25% combo, or 19% with 1 meter (which he can Clash, wasting your meter in the process). If Sword Spin doesn't come out as a wakeup attack, you will eat another 30%+ combo. This will continue until you can get the stupid fucking wakeup system to work. If Superman reads that you will attempt a Sword Spin, wakeup or otherwise, he can simply do a jumping attack into a 30%+ combo. The only way to avoid this is to wakeup Sword Flip, which is never a good idea. Backdash isn't an option because Superman's f23 will catch it, leading into a 30%+ combo.
Pushblocking is a great option against most of the cast, but not Superman. The distance he gets pushblocked is horrible for DS. Gunshots are too negative on hit and block to be viable options. At best, you hit, deliver 6% damage, and are left at disadvantage. At worst, he air-dashes and delivers a 30%+ combo while going back to bulldozing you with f23. You can try a j3, but he can punish this on reaction with a 30%+ combo. You can throw out a random Sword Flip, which will either deal 4% against an airborne Superman and not get a hard knockdown, or it will be blocked and punished with a 30%+ combo. And that's about it. Once you pushblock from the corner, you literally have no choice but to let Superman do whatever the fuck he wants, and attempt to react accordingly. Guess wrong and you eat a combo and are stuck back in the corner.
2. From midscreen, Superman's options beat anything Deathstroke can throw at him. I have literally been punched out of Sword Spin, mid-animation. Deathstroke's backdash does almost nothing against Superman, and you have to constantly be on the lookout for his low grab. Once he gets within range of his f23 pressure, it's a straight-up 50/50 game that leads to 30%+ combos. As always, you can pushblock to avoid his 50/50, but this is only a minor inconvenience to Superman, while it basically shuts down all of Deathstroke's options. As far as I can tell, Deathstroke has no way to get out of Superman's Super Breath frametrap, except with pushblock.
Attempting to MB a f3 or b3 is dangerous because Superman's f23 can break armor, even without his trait, leading to a 30%+ combo.
If you do manage to land a hit, you better make the most of it because you have to respect Superman's wakeup game. He's got at least 3 fully-invincible wakeup options (air grab, low grab, and flying punch). Low grab and punch are punishable if you can bait them out. However, if he doesn't take the bait then you are stuck within his f23 pressure range.
His f2 comes out in 8 frames, but seems to dominate a lot of faster moves. One of my friends starts out every match with f23. If I do anything other than jump or block, I eat it every time. Even if I start with my 7-frame Sword Spin, 7-frame Sword Flip, or backdash, the f23 beats me and I eat a 30%+ combo. If you are even remotely late following up one of your blocked f3, b3, or j3, all of which have massive block advantage, you will eat the f2.
Gunshots are extremely dangerous to use from midscreen. They can be used to keep Superman in check, and to keep him out of the air if you can predict his jumps, but that's about it. At best, you hit and deal 6% damage and are left at disadvantage. At worst, he air-dashes over or ground-dashes under and you eat a 30%+ combo.
3. From full-screen it becomes a game of reads, however Superman does more damage. Thus it is up to the Deathstroke player to make the most correct reads, as a single bad gunshot can cost him up to 18% health. If Superman has full meter, the Deathstroke player literally can't make a move without suffering the wrath of Superman's 2-frame super move. From anywhere except absolutely full-screen, Superman can reversal a block gunshot with his super for up to 44% if his trait is active.
If you do start to win the zoning war, Superman can close the gap whenever he chooses. All he needs is a single knockdown or whiffed gunshot and get can get into f23 range.
Long story, short: Superman shuts down all of Deathstroke's options, except from absolutely full-screen, and even then it's a pretty evenly-matched fight, and Superman can easily close the gap with minimal effort. Every move Deathstroke makes is a total risk that, if punished, will lead to him taking 30%+ damage and being put in a disadvantageous position. Every move Superman makes is basically safe. Deathstroke literally has no defense against f23 pressure because pushblocking keeps him at just as much disadvantage as just eating the chip and guessing the 50/50.
Finally, d1 is one of the few pokes that can punish f23. However, because the input for Deathstroke's Low Shot is bd1, he is very likely to do Low Shot instead of d1, which will cause him to eat a full combo.
or 
?
to D1 instead?