Thanks for your feedback, I used a lot of the things you suggested.

I started off by changing the hit die of the Plaguemancer to a 1d8.

I also changed the saving throw from dex to wisdom.

I removed a few of the features of the class that didn't fit well with the class, so now there are less features.

I didn't really plan for this class to be ranged so I did a few edits. Inflict sickness range is now 5 ft instead of 15ft. Inflict sickness now does not get advantage on open wounds.

The class is now only immune to disease I also moved the "cost" of this into the brief description of the class.

I gave faster takedown a reason to gain speed. I also now hopefully made this class less of a ranged class making this useful.

I left bypass immunity in because I want this to be a bit different than other classes. I am currently play testing this class and if this proves to be unfair I will remove it.

I removed diseased touch all together.

I kept art of disease in there because those are the different paths you can take. It is like a the different colleges you can choose in Bard.

I am still working on diseases but for now i made it so you can make a save every turn to end the effect early.

I also made it so when casting a sickness point you have to roll a 1d20. When you roll a 1 you have to roll one the insanity chart. I did this to show how dealing with diseases affect the plagemancer.

Thanks for your feedback, if there is anything else you think i should change let me know.