Well, as they say in the BTAS episode "The Trial", without Batman the gimmicks would have been different, but they'd probably still have been out there causing chaos.
So instead of focussing on Batman and upping his game repeatedly to challenge him, the Joker (after possibly dealing with the security guard/policeman/fellow crook who caused him to fall into the acid) seems a lot less of a threat, essentially becoming a Fagin style character rather than the world feared "Clown Prince of Crime". With Batman you NEED to be the best to be a recurring threat, Mr J here hasn't got that impetus.