Exactly. This is another reason to turn autopromote off. If you plan on using your army for strictly defense and deterrence, then promotions like City Raider are pretty much useless, because you won't be attacking enemy cities. Except for defending critical resources on hills, Guerrilla and Woodsman will also lose importance, since your army won't be attacked while marching through enemy territory. Concentrate on catapults with barrage, axes/crossbows with Combat and Shock, spears and pikes with Combat and Formation, etc. I think the AI will try to give you a "good rounding" of promotions, which is bad for two reasons. 1. You are using your army for a specialized purpose, and 2. Civ is a game where you want to have a well rounded army of specialists (and a well rounded empire of specialized cities). For examples, I want my axes to do nothing but fight melee units, so I only give them Combat and Shock. I want my spears to only fight mounted units, so I only give them Combat and Formation. I want my swords to only take cities, so I only give them City Raider. The reason this works is that your stack/army will select the strongest unit to defend against the given attacker, so unless you get hit with so many mounted units that you run out of undamaged spears/pikes, your spears/pikes will always be the unit chosen to defend against mounties.
For an army attacking another army, it might be helpful to have better rounded units so that they wouldn't be helpless against whatever defender the enemy sent up (a spear with Shock would do well against either a horse archer or another spear). However, if you get to throw the first stone (which usually means you're defending your territory and have access to roads) you can just pummel the enemy with barrage catapults.
I did not realize he is using gold edition in my last answer - rather interesting with regards to my short term memory 
