Have doctors historically been confident in the medical practices of the time, or have we always been aware of the flaws?

My grandmother recently gave me the book The Housewife's remedies and good advice published in 1934 (Original Swedish title: Husmoderns hemkurer och goda råd by Kerstin Wennström) which contains advice for women on how to cure certain illnesses. A lot of the advice is very bad, for example: The book gives the advice that if someone suffers from a sore throat, it is good to drink a mix of hot water, honey and turpentine(!). If it is a small child, you should use smaller amounts of turpentine.

Now today we know that this is not very good for sore throats or people in general, but did people really not know better at the time? Or were doctors aware of the problems in these so-called remedies, but thought them the best solution? I'm also thinking of practices such as draining the patient of blood. Did doctors really think that was a great way of curing sickness, or was it more like we view chemo today, a bad solution to an even worse problem?

This is my first post on reddit so I'm still figuring this out. If I have made any mistakes or this post is in some way wrong please tell me so I can do better in the future!