Mechanically, Rolleiflexes are simply better built than Autocords (and Autocords are better built than YashicaMats). The finish on the parts is better, the solidity, fit. Also the 'Flex is made to be repaired, adjusted, have parts replaced, etc. in ways that the Autocord isn't.This isn't to say that the Autocord is poorly made, it isn't. But there is not denying that Rollei used better materials, executed parts to a higher level, and shows a combination of engineering and design through out that the Autocord doesn't match. The strap lugs of a Rolleiflex are a good indicator of the overall difference- the Autocord is well-made, the Rollei has an extra layer of elegance and attention to detail beyond the technical.
I used an Autocord and a Rolleiflex 2.8C concurrently for many years. the Autocord was more of a knapsack shooter. The Rollei was more of a 'I am going out to take photos' shooter. Except in cases where I was going to be in places or situations where there was a chance of theft or a need for quick reactions (political marches and such). The Xenotar has more bite. The Autocrd Rokkor has better OOF. The bite and contrast of the Xenotar worked well with the creamier quality of Fuji ACROS. The Autocord was a little flat with ACROS but worked very well with Delta or TMax films.
Some day I hope to install a Xenotar or Planar lens set on an Autocord body. I love the focus system and the overall feel of the Autocrd is very nice. The 75mm lenses from a Rollei will fit the Autocord easily, and it's be easy to machine a mount for the 2.8 viewing lens.