Definition and Purpose of an OS - https://en.wikipedia.org/wiki/Operating_system#Definition_an...

I am not sure what you are arguing here. The above definition + the previous link to distributed OS where the motivations for the same are listed establish the "reason". If you find other approaches more palatable that is fine (provided you know what you are doing) but the original blanket statement you made viz. "This type of thing always seemed to be in the very cool but pointless basket, to me ... I think a lot of effort was wasted chasing that dragon. Wasted is probably the wrong word because research into cool things is good and probably created useful things along the way. I don't feel there was ever enough justification put into it and it could possibly have been better spent though." is wrong.

> There are many layers and components, and functionality can be implemented in many different ways in different levels of these things.

All implementations are not equivalent w.r.t. all parameters; hence the various tradeoffs in competing designs.