Also, if cancer and other diseases are supposed to exist and kill people for some kind of purpose we don’t understand, why do we have the ability to treat, vaccinate and cure those same diseases

Oh god, now you've hit on why some of the sects that we consider cults do what they do. Somehow, wearing clothes, using plows, building structures to provide shelter and warehousing, creating roads that wheeled contraptions (but they don't have engines!) use, etc., etc., as part of our technological lives isn't a sin, but using medical advancements is!