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Late game battles you need 1-2 turns to set up your units IN THE combat. This becomes frustrating when you have to do it every single combat, specially with how huge they are. I remember devs said they are not adding pre-battle unit positioning because they want to make combat take less time. Since nowadays late game combat takes A LONG time to finish anyway, what is the point of having to reposition armies FOR EACH battle? I think that would be a good idea.
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You need to be able to choose which of your 5-6 armies in the area should enter the battle, the game should not choose the 3 strongest for you.
#The game needs pre-battle unit positioning + Army selection for battle
compact nimbus
ashen cargo
I duuno man, sound like an abysmal chore to me. The most I would agree to would be to drag them around like stacks. To decide army on the left right & middle. I think its determined by how you atack on the world map, they can make it more obvious
shadow flower
I kinda get Point 1, but cant really unterstand why its a problem for you, that the game decides for your 3 strongest armys to enter combat.
The only thing that comes to mind is, that you would want to "sacrifice" your 3 "weaker" armies first, to attack the enemy with the stronger ones afterwards.
For myself, i tend to attack smaller stacks of a larger army all the time, to make my fights easier:
I would totally agree if you wanted a chance to prevent your armies to get drawn into a vassals battle, when they get attacked.
That happened to me quite some times, and seemed like you cannot just say, "you dont take my armies with you", when a free city party is raiding nearby and gets attacked, with you armies in range.
Im normally trying to attack with only 3 Armies in the first place, to prevent smaller stacks from being focused first. Either my three stacks got depleted and are less strong because of an earlier fight, or there is no option for the enemy to attack anything, but my strongest armies, since they are the only ones around.
Might be missing the point there, so could you please try to elaborate, why you would like to choose armys, that are not your strongest for a fight? Maybe im just missing your good reason for it 
mossy iron
I kinda get Point 1, but cant really unterstand why its a problem for you, that ...
going further, I think we need a rule which prevents this behaviour, it seems very cheesy.
I.e. doesn't matter whichever army you attack 3 strongest ones are chosen anyway to defend (in the range of reinforcement). So, the army you attack is not forced to be in the fight if there are stronger armies around.