I see two ways to compare objectively.
First: To compare armies, you should not only review their strongest composion possible, but also their avarange potential on an competetive level. That needs a lot knowledge about all battletomes and their strength.
Second: Different game sizes mean different strength. Some Armies shine on 1000p, while others prefer 1500-2000. A few are very strong on any cap.
Terrain and endless spells are not important for the armies strenght itself.
For example. I see LoN very strong. Especially on small games it benefits from the smaller battlefield, what makes graves much stronger.