The midi range, not the tweeter, is the most important driver in a speaker.

yes, the mid is the most critical and at the same time it is the most compromised by standard passive crossovers.

This reminds me of Seinfeld - "The top button makes or breaks the shirt".

This is wrong. If mids were the most important why dont you just buy yourself a pair of ATC midrange domes and stick them on some stands and call it a day? 
That would never sound high end. 

There is no such thing as the most important driver. Every driver is equally important DO NOT BE FOOLED

Unless the integration with box, XO & other drivers  is so egregious that it makes no difference that any POS would be equally as awful.

What about a 2 way 2k XO?

They are plenty of loudspeakers of yore that only had a great midrange and are considered world class. Quads, Apogees to name a few. If you get the midrange right in a loudspeaker you may not need anything else.