>>713200972 (OP)It's about understanding what units are for what purpose
Spears are good at holding a line and will annihilate cavalry
Swords are good at killing spearmen, but get obliterated by cavalry
Heavily armored units of these types are better at their respective roles
Axe/Club or other forms of assault infantry are good at striking above their weight, killing armored units, but are less effective at spears or swords for holding/infantry clearing - but some times are absolutely necessary if going against a armor heavy faction like the Romans in RTW1/2 or Chaos in TWWH.
Archers are mainly used for harassing cavalry, particularly missile cavalry like horse archers, or tipping the line battle in favor - use them to soften up elite units that will be trouble during the line melee.
Cavalry units function similarly - cav units with spears beat cav units without spears, cav units with swords kill infantry quicker - but there's a bit more nuance, since cavalry with lances are better at killing units that are stationary - but only if used properly in cycle charges.
Horse archers and skirmisher units like javelinmen are best used to flank and harass the sides of formations and get units to split off and isolate - horse archers doing what normal skirmishers do, but for cavalry, since foot skirmishers typically get folded by cav very quickly.