With the prices of Leica these days, people who buy them ought to be concerned about shutter quality and body quality. Certainly people aren't buying them for the 1/50 flash sync or the accuracy of the cloth shutter compared to the Zeiss electronic shutter.
A Leica is now like a mechanical Swiss watch. While Swiss watches are used on a daily basis to tell time, they are certainly not as accurate as a $9.99 Timex. So the argument to buy a Leica is not just about features or specs. It has to do with perceived quality, luxury and reliability/longevity. So when one compares to a ZI, that has to be taken into account.
I would make it simple-- if you want features/specs, go for Bessa R2/R3/R4, if you want quality, luxury, reliability, longevity-- go for Leica. ZI sits in the middle between the Bessas and the Leicas.