[squirt]

> Zaner-Bloser or D'Nealian, which both derive from Palmer.

This is not accurate. Zaner predates Palmer.

> Both of them are terrible. They have indistinct letter shapes that degrade horribly when written quickly.

I would more attribute this to...

  1. Unskilled modern penman
  2. An eye that's unaccustomed to reading old script

... rather than something intrinsic to the style. Business penmanship was, after all, created to be fast & legible. Historical pieces of penmanship are most often legible, particularly when written by skilled penmen.

Source: was professional penman, specifically studying 1860-1920 American penmanship.