Confusing City Income Display

Why is army upkeep taken out of cities as a factor of population? I understand the concept, I just don't understand how seeing that huge negative number on your largest cities possibly helps anyone when playing the game. Is there a way to change it so it displays the RAW income of each city (before army upkeep)? This would be much more useful to me, allowing me to see at a glance which cities were valuable enough to defend heavily and where to place my high-skill governors.
Is there anyone who can explain to me how the current display is helpful? Am I missing something?

You have to check out the city details screen. This will let you see the gross income (broken down by agriculture, mining, trade, etc.) as well as your expenses (similarily divied up). I think this is the closest you're going to get to what you want to see.

Is there a mod to change this, perhaps?