i'm not sure of his frame data, it might have changed but here is my basic gameplan on zoning:
Check with iAGS to prevent jumps, once you opp respects your air control work in low shots, When your lows get blocked either Ex them or Wait for a reaction then check them with iAGS again or use the machine gun to hit mid, MB the machine gun to keep them honest so they don't get in a rhythm of blocking and dashing or ducking after every shot. Quick shot also stops dash ins pretty well and recovers faster than his other grounded projectiles.
Notes: ex any gun works well to throw of the pattern and halts you opps progress, Deathstroke builds meter so fast that its definitely worth using often.
His trait is a risky tool, but i find its best used after a full screen knockdown and followed by use of the machine gun so your unblockable bullets will be hitting mid and deal a solid amount of damage, they would have to jump or teleport to get out so that read is up to you to capitalize on