I don’t want to establish a new world record for the smallest waist. A well fitting corset can be very tight without being uncomfortable, but the waist reduction should not be so great that the proportions are spoiled.
This is, of course, a matter of taste, but I think there are some general aesthetic principles which should be adhered to. I do like the early pictures of Ethel Granger, Cathie Jung or Spook very much. Unfortunately by aiming at extreme waistlines they lose much of their aesthetics (in my opinion).
Just as well I would not like to attack or judge anyone who has different viewpoints. Corsets are often presented in conjunction with Latex-S/M-Fetish stuff. This is totally o.k., but I think this will not promote the usage of corsets in the public as a functional and accepted (yet erotic) piece of clothing.