They tangle before and Black Mask came out on top.
The point is - The writer drives the character.
There are stories where Joker goes on a rampage just to give a random dude $10,000 in cash. Then there are stories where he kills nuns with rubber chickens and tuna sandwiches.
Then you have Blackmask who will use a kid as a bat to bust up her parents of the kid because THEIR FRIEND owes him money. Then you have stories where he won't kill a kid....again the writer is in control.