I hope that heavy armour and shields will significantly lower Initiative, and require a certain Strength to use - in WoM, there were no penalties for using the best, heaviest armour - so if you had enough gold, all your champions (be they Level 1 or 5) would just get kitted out in the best stuff available - which made no sense at all, and pretty much turned each one into the same, identical-looking tank.
These have pretty much been confirmed in the following links.
https://forums.elementalgame.com/409834 - Dev Journal on Armies
https://forums.elementalgame.com/407109 - Dev Journal on Weapons
If you look at the actual spreadsheet on the Weapons page it shows speed penalties for heavy weapons. The encumber system also allows stronger units to use heavier or more gear. While weak ones have to pick and choose.