Jiang Chen had the recipe and the necessary ingredients, which he had harvested in the ancient herb garden, to concoct the antidote. Put plainly, it was impossible for another antidote for this particular Miasma to be produced on this island.
Once he finished refining the antidote, it wouldn’t matter how many sky rank and earth rank herbs the other people had obtained, the final distribution would still be up to him. If they didn’t cooperate, Jiang Chen wouldn’t mind ‘accidentally’ dropping the antidote into the lake. Only the members from his sect could count on his benevolence.
It was obvious this island was full of peculiarities with restrictions seemingly all around. However, these restrictions’ only function was to scare people. Those who moved with caution and patience wouldn’t find their lives put in danger in the herb garden, since the killing power of the formations had decreased. This was also the reason the sects were able to enter the island.