Ok this problem existed in Galciv2 as well:
The AI keeps designing and building units with no armor. And you just crash his armies with your troops that can take damage.
I understand that this might also be part of a shock troop strategy where the best weapon is chosen to build inexpensive troops, but even in such a doctrine, one needs units with armor as well.
The loss of one's units is a bad thing. This is especially true during the start of the game were units and resources are scarce. This is also especially true since units can accumulate xp which become HP. A full armored unit with leather and 3-4 levels can survive many units of unarmored shock troops of same level. This is also more true since there is an army stack size limit: you can't just just mass attack with loads of shock troops to get a combat advantage, you have to do it in waves and this wastes the excess shock troops that don't attack.
Right now you can survive in any game just by focusing on armor tech. The AI has a blind spot about it.