What If Deathstroke did to Batman what Ock did to Spider-Man
What if Slade some how switched bodies with Batman and then destroyed his former body with Wayne in it, How would that change things? How would Slade do as Batman? So its a vs in that can Slade do a better job as Batman then Wayne and how long do you think it would last? Also would the JLA knowing that Wayne died in Slades body put away Slade or would they try and deal with it?
And on the whole, no, he wouldn't do a better job as Batman than Bruce. Tactically speaking, he'd be fine, but Slade's a master assassin/soldier/mercenary. Actually solving crimes isn't his forte.
That in of itself would cause problems. The Bat Family alone would attempt to bring him down and know pretty quickly that something's not right with "Bruce". That's without the League being drawn in.
You asked in the OP if Slade can do a better job as Batman than Bruce, correct? Regardless of whether Bruce can come back or not, Slade isn't going to do a better job of being Batman.
Sure, he'll kill criminals, but that in of itself won't make him better (and really, considering what Batman is about as a symbol, most definitely worse). A lot of what Batman does isn't just kicking bad guy's asses. He solves crimes and unravels clues to bigger threats. Slade, while exceptional when it comes to waging war and combat, isn't a detective.
All in all, the question is subjective as is the term "better", but Gotham City certainly won't be better off with Slade running around than Bruce.
If this is the same situation as spiderman doesn't Wade get memories? He isn't stupid or have such a overbearing personality as Ock. I think he could easily pluck those memories out Being used to accessing 90% of his brain and act the part as convincingly as possible. Won't last forever but he can play the role to avoid suspicion for some time.
It will end just like things with the avengers for spidey. He will take advantage of his knowledge of the criminal element and his own skill set and brutally take crime down. Maybe not kill with the mental block of Bruce in his head (you said same situation so I'm using same situation) but he would leave amputees and broken men in his wake. If/when he helps the justice league they will notice so either they, the bat family or the combination of both take him down.
He will clear alot of crime from gotham but as the 'rules' are thrown out the window it will only escalate to a higher and more violent degree later on.