Answer:
I agree with this statement to some extent.
In Pasteur's germ theory, he suggested that the spread of microorganisms in the body were what caused disease. This turned out to be true, and would lead to advancements in medicine - specifically in prevention of and treatment of diseases, as physicians and scientists would be able to treat the microorganisms causing the problem.
Not only that, but it also led to Robert Koch isolating the microorganisms that caused multiple diseases that were rampant at the time, including tuberculosis and cholera. Koch's research then led to the research of and creation of more vaccines that put a stop to the massive death rates of these diseases, especially in highly-populated areas which were incredibly vulnerable to these illnesses. ( E.g. London).
However, Pasteur's germ theory was not believed by many people, who still believed in other explanations for disease, such as spontaneous generation. One of these individuals was Henry Bastion, who was a prominent and well-trusted English physician at the time; he openly voiced his disagreement with Pasteur. Due to this, germ theory was not widely believed until later on in this period, which led to many physicians not adapting their diagnosis and treatment around germ theory for a long time until it was widely accepted in the 1890s.
Another reason I disagree is due to the discovery of the smallpox vaccine by Edward Jenner. Jenner's vaccine, which was an injection of cowpox (a safe variant of smallpox) was the world's first vaccine. His discovery helped to decrease the death rate of smallpox which, at that time, was a highly deadly and incurable disease. The smallpox vaccination led to the research of other vaccines and was arguably another big turning point in medicine in 1700 to 1900.
In conclusion, I somewhat agree with Pasteur's germ theory being the biggest point in medicine in the period given, due to it's impact on how we understood disease and it being the foundation of Koch's discoveries, however the opposition to germ theory and Jenner's smallpox vaccination lessen the impact that it had up until the late 1800s at least.
Note:
Hope this is okay, I last did a history question a year ago! :)
