[RugnirViking]

A)

Leeches are often used in literal modern hospitals in the developed world as an effective treatment for certain ills.

B)

If we had no alternative, we should stick to it, but look at other things in the meantime. You seem to be advocating doing nothing at all, which is trivially easy to show works for no-one

[emodendroket]

Yes, leeches have extremely limited use. However, bloodletting and leeches killed far more people than they ever "treated."