Ok so I don't play Joker so maybe I'm wrong. But its hard for me to accept the character being as bad as you say based on what I've seen from players. He seems like a decent mid-tier character. At the very least hes a lot better than swamp thing.IMO
Joker:
1. 50/50 mix ups pressure(2/5) - Joker has a hard time opening an opponent for his BNBs. He has a nice low into overhead that can be used (B1 - crowbar), but it is slow enough to block on reaction and has to be set up. The mix ups he has do not lead into his damaging combos or set ups. But his corner pressure is insane due to his teeth set ups. He has hard to blockables but they are too situational IMO. He opens his opponents up with his J2.
2. Zoning and anti-Zoning(2/5) - His gun shot is a nice tool to catch back dashers or jumpers but it has to be used carefully since it's easy to punish. Since it doesn't kockdown on hit anymore its best used for meter building or punishing. His teeth can help to create space but joker needs to be close to the opponent. He gets zoned out very easily.
3. Neutral game and footsies(1/5) - This is the weakest part of his game IMO. In order to start his pressure he needs a knockdown just like in Inj 1. His b1 - 3 gives him a hard knockdown where he starts his teeth setups and pressure. But in order to get to this point you have to find a way to open the opponent up. His strings are pretty slow so you cant really pressure the opponent until he is on the ground.
4. Defensive Options(1/5) - Joker is definitely not a defensive character. He does not have a good wakeup and your best bet is to block correctly when knocked down. It is very hard to get someone off of you when they start their pressure. Inj 1 had acid flower which covered this but he does not have this anymore. His new parry is very good but it only works on highs and not lows.
5. Damage Output(5/5) - Joker's damage is insane. His BNBs include MB RLG. If you land this he can hit you for 49% easily as well as set up a hard knockdown. His new super allows for a follow combo and has way more damage this time around. You can get around 70% damage if you land his super.
Total Rating(11/25)
If 'Fun' was a rating it would be (5/5). Other joker mains feel free to chime in this is just my take on the character.
I don't think there's anyway you can justify saying his neutral and defensive options are both 1/5.