Armor is also needed in the regular melee once stronger weapons are introduced.
Armor can make a big difference. It can decide if you win or loose the unit, regardless of the outcome of the battle. And you won't always get the first blow.
I also noted the spear maiden, but at that stage My *army* was in better armor. And I wasn't focused on an Armor rush tech strategy either.. I was just researching all the affordable tech.
There is always the issue with the Army amortization cost. That is the cost in time and wages that a unit will spend until it gets to the front, i.e. is used in battle. Once you factor this cost in the equation, building shock troops instead or armored troops is a waste of time and resources. Also factor in experience from survivability... it's a lost cause.
I get the feeling that the AI doesn't protect it's armies... It's like it thinks that units are built to be thrown to the fight.
The same argument holds for Galciv2 The AI never prioritized or built units with defenses, until it was too late...