Oh boy... Where do I start with this matchup.
It is 6-4 Bane in my opinion but other Deathstroke mains say it's even.
Deathstroke's saving grace in the matchup is that his keep away game with guns can be decently effective to keep him away from you; now he will get in eventually and when he does, make sure you are not pushed into the corner. If Bane knocks you down in the corner, GGs.
I find that raw sword spins to break banes armor are the most effective as well when he gets up close with venom. There may be other options that are better, if other DS mains wanna chime in I'm all ears.
Unfortunately Deathstroke's oki is pretty useless on Bane because of his godlike wakeups with venom. This also means Deathstrokes corner game is not very useful against him either.
It comes down to smart reads and staying as far away from bane as possible, especially when he has level 3 venom up. If he's level 3, don't bother trying to attack him. Just run away.