Dennis O'Neill returning the Joker to his murderous roots with "The Joker's 5 Way Revenge" in Batman 251 probably made the character remain relevant throughout the 80s, 90s, and 00s as comic books increasingly became more "dark and gritty". However I don't think keeping with this creative decision makes sense from a narrative standpoint. The Joker has killed so many people at this point in the comics that one has to question why he hasn't been given the death penalty* or killed by a rogue police officer of vigilante.

When it comes to the Joker I much prefer the eccentric "Clown Prince of Crime" to the mass murdering psychopath take on him. It goes to show that the more "dark" direction isn't always the one that's more believable.