And there are many other example of people doing things in a way that was at best bad and at worst actively harmful for hundreds of years until somewhat recently.

There's a minor logical flaw here: If things were, indeed, 'at best bad and at worst actively harmful'...how did humans survive for that long? Suffice it to say that the popular view of medicine in the pre-modern eras, of people's intelligence in general, and of just about gat dang everything, is off at best.

Further, considering that we have anti-vaxxers, conspiracy theorists, Flat Earthers, and similar such beliefs today, I take leave to slap a giant [citation needed] on the human of 2022 AD being any 'smarter' than the human of 1022 AD or 1022 BC.

Let's address the question you're pointing to in your text, ie, pre-modern medicine, and you can see just how it was, with these previous posts:

• u/BedsideRounds has a non-exhaustive list of Stuff That Worked;

u/sunagainstgold talks about:

• medicine and its efficacy;
• medical education in the Late Middle Ages;
• and various solutions to the removal of arrows, including the case of Henry V.

But the star of this post is u/BRIStoneman drawing from the 9th Century medical text Bald's Leechbook:

• On the book's attitude to the treatment of medical conditions in general;
• On the treatment of infected wounds;
• On its recommendations for cuts and fevers (with bonus literacy downthread);
• An assortment of treatments demonstrating that the leeches of Early Medieval England were on to something;
• On its treatments for worms of all kinds;
• On its treatments for eye infections, including one that, surprisingly, works against MRSA.

Bonus: Bald's Leechbook is available in all its digitised glory here.

To add to the links providing by DanKensington

u/wotan_weevil on why blood letting lasted so long

u/BedsideRounds wrote and podcasted on blood letting

It seemed to work, it fitted in with their understanding of how the human body worked.

A lot of olden medicine still makes sense now (for my ancient era: too much alcohol is bad, exercise like callisthenics is important, taking the pulse as a diagnostic tool, acupuncture, surgeries were performed, emetics, power of emotions and so on). Not all worked, charmed water was not much help in an epidemic but any stupider then some of the pandemic non-cures we have seen in last few years? The belief in nourishing one's essence saw some practises that one would not recommend today but the idea of control and close to nature to improve the essence meant the ideas would have made sense. People with ye olden medicine seem to remember the bits that haven't aged well, they forgot the contexts of the time for why they thought this was the way to treat it and the stuff that worked.

I would advise against modern people smart, the ye old past=stupidity. People of our time, (as Dan points out) can hold some....intresting opinions and I would gently suggest we haven't reached a utopia where people aren't doing harmful things to the planet, others or themselves.

If your looking at the past and thinking the people were dumb, something had gone wrong, some information and context has been missed that should explain the logic of why something happened, about the way people lived and the contexts in which they took decisions. Yes people sometimes did stupid things but then, we do so nowadays (or at least I hope I'm not the early person here who has something stupid). If your thinking there dumb, you have missed the practical steps people took in their lives to deal with the challenges of their time and the achievements of the past in so many spheres.