I don't think there's any argument that they look like two different cars stuck together... As for "what were they thinking" it might have been a band of glass that goes up and over and all the way across the roof to meet the window the other side.
They are interesting to look at, in a good way as well as being "interesting" and much nicer in the metal than photos. My personal taste: I much prefer with bumpers on to off.
This is the "what might have been":
https://www.classicdriver.com/en/article/cars/beauty-lancia-sport-zagato-prototipo-lies-withinThere was always the PF or Vignale. I've just finished the new Fulvia/Flavia book and was reminded that the Zagato was cheaper than the others. That might have been demand and supply, and "rare for good reason" might also be applied
Quality of build, paint, corrosion, strength, and I'm sure "niggles" make them the worst of the lot. Colin always says something along the lines of "they were built to make a statement for a year or so, nobody expected any to still be about 60 years on".