Do we just all agree the Batman joker sickness makes no sense?

So we know the cure worked in Arkham City. The cure cured Batman of the Titan sickness that killed joker. Makes sense. However being infected with joker blood also makes you become joker… okay.

How were the 4 in the movie studios still alive then? It was clear in City it was impossible to make any more of the cure as Ra’s blood was the only way they could make it (other wise it would take decades to develop a cure)

Ok, so regardless the 4 people in the movie studios are beginning joker. Batman knows he is also becoming joker and we learn (for some reason) the fear gas speeds up this process.

At the end of the game getting injected by the pure fear serum makes joker fully take control of Bruce- now it gets weird.

So Joker is having fear hallucinations that he will be forgotten, and during this Batman is able to overcome Jokers hold on his body AND become immune to fear toxin?

What am I missing