[Suggestion] Harsher penalties for encumbrance
I think an issue with the unit designer is that the penalties for encumbrance is minor compared to the gains from more armor, at least for melee. A melee unit at 80% encumbrance (more armor) is almost always better than a unit with the same traits at 40% encumbrance and +2 initiative. This leads to armies that are dominated by melee troops with the heaviest possible armor, since they have superior or equal survivability in every scenario.
I think a good penalty for encumbrance would be to give a vulnerability to being knocked prone, since with heavier equipment it will be more difficult to get up if you ever get knocked down. Something like a 20% for medium and a 40% for heavy encumbrance . Mounts should also no longer provide 100% prone resistance, which makes prone attacks completely useless against players, who usually field all mounted units from mid game on. This bonus will not be completely removed from mounts, since the +20 weight limit will usually move the unit to a lighter encumbrance penalty, resulting in less prone vulnerability. A side effect of this will be a buff to the mace line of weaponry, which will become much more useful against heavily armored/weighted units. This should allow maces to be more competitive against swords/spears lines of weaponry, especially in the late game where plate armor renders them obsolete currently.
Another possibility is to have encumbrance penalties for other stats, such as 10% hp penalty for medium and 20% for heavy. This will make lightly weighted units more effective against mage units/tactical spells/armor ignoring attacks/curse than their heavier counterparts. This will at least give some tactical advantage to having light troops other than their recruitment cost.