I don't think this is a rant... And I understand the game is complicated, but why isn't the manual written from a users perspective?
As an example...
Certainly a candidate for the most important rule in the game: "In order to receive supply... the combat unit must be within both five hexes and twenty MPs of the applicable headquarters unit. In order for a headquarters unit to provide supply to its attached combat and support units, it in turn must be within both 25 hexes and 100 MPs of a railhead."
What page of the manual do you think the rule appears on? Page 1? Page 23? In the first half of the manual? No, no, and no. The rule appears on page 198.
It doesn't even appear until page 7 of the supply section!? Before getting to this most important of rules, you have to wade through the uninteresting and unimportant "vehicle shortage modifier" and the automation of "emergency vehicle reallocation." How can it be more important to tell us about an automated process over which the player has NO INPUT OR IMPACT than describe the most fundamental of supply mechanisms??
The whole manual is written like this! It is as though the authors are more interested in cataloging every intricacy that they have included in the software - or in other words, telling us how clever they are, rather than telling the player how to play the game.
Another example - the section on Air Mission rules, opens up with a list of factors affecting plane mileage - cruise speed, morale, HQ location. WHO CARES? The single most important thing to tell a new player is that certain types of air missions can be automated, but some cannot be, and what do I gain and lose by fiddling with this manually?
OK, I lied, this is a rant.
The root cause of your frustration (IMHO) is that players expect documentation to serve 2 purposes - a learning guide, and a reference manual. And it's damn near impossible for a technical writer to do both at the same time.