The redeeming quality TBWL has is that he's not currently over used and is kept as an event villain and a cosmic one at that. On top of being a fanfic sutpid and badly written character Joker is crap because he is also overused and writers feel entitled to put him in bad stories without explanation on how he achieves thing other than "he's crazy".
Batman is meh. The Joker is ugh. But the combination of both is actually somewhat less insufferable, while still pretty uninteresting deep down: he has no motivations no rime or reason to his actions, he has no limits etc. etc.