I think you are overstating just how successful St Domingue was in the 18th Century. Whilst there was a period in the early 18th Century during which it was producing 40% or so of the worlds sugar and coffee consumption I think its important to note that this was produced almost entirely by slaves. from wikipedia: "...slave population in 1789 totalled 500,000, ruled over by a white population that numbered only 32,000." So I"d say that the MEDIAN wealth of the population has arguably considerably INCREASED since 1790 since they at least now own themselves.