You're right. Back then when people wore Dior, Balenciaga, Givenchy, or Yves Saint Laurent, people knew from a distance who they were wearing because each designer had different ways of styling, workmanship, and ofcourse overall design. Now designers have succumbed to trends that you'll probably have to look at style.com to see who the designer is that created that specific jacket, dress, or pants since many of them look the same.
Think of it this way; look at the book with focused eyes, the words are all separate and distinguishable; that's the fashion of the past. Now if you look at the same book with crossed-eyes, the words are blurry and interconnected, undistinguishable from one another; that's the fashion of today, but you'll notice that some words still do stand out.... that's Margiela and Alaia for you.