Well, even in the most minimalistic approach : Even these recordings are multi-track by nature.Someone has to decide that Mic1 should be routed to the left front channel, Mic 4 to the right rear channel, and to balance out their levels. Microphones don’t know these things by themselves ;-).
This is normally done on devices called Mixing consoles.
If you don’t like to call this process ‘mixing’, that’s fine with me. But I think you understood what I meant, right ?
Upmixing something from mono to multichannel is often indeed not very useful. Especially for ‘acoustical’ events like Kind of Blue.
However : even a mono recording can have multi-tracks as a source. (Seperate bass, separate trumpet, etc).
A good engineer can do wonderful things to such a mix.
(Especially with more ‘electronic’ music, where there is no such thing as ‘staying close to the original event’).