I wouldnt call relationship low/high lvl units so unbalanced as you ppl say it is.
Early game you can lead only couple of 5th lvl units because leadership requirements, and low lvl are your basic power. Later whit more leadership 5th lvls take over that role but still there is no way to compare dmg output of 1-2 lvls with 5th. It all depends of what you want of your army : survivability, tanking while kil enemy with spells, or other . . .
Low lvl units are not suposed to be used with mage, their strenght is in numbers(leadership) and +1dmg items, hight lvl are best for mage due to double cast and high % phantom spell (virtualy doubling army).
I managed 480000 crit with lake fairies and gorgunas once, that is simply not possible with any high lvl unit no matter what buff/debuf you use (girl power build and item set-initiative 13, speed 7, dmg 4-6 on 1st lvl unit).
All i want to say no need to rebalance low/high lvl units, because they all have their roles throughout game, it`s only question what you as player and their commander want of them. No1 can play shrek build and 100% crit archer at same time, just make your mind and lead army, if you want to change 5 reserve slots will be of great help, but keeping 2 diferent army build is simply bad commander
