The AI is a big spammer of troops. For basically any faction I've played against, the AI spams one or two designs (generally whatever becomes available with Training (e.g. Spikes of Krax, Gray March) and whatever becomes available with Weaponry and Leatherworking (lot of Spear Maidens here, Defenders, etc.). It has tons, and tons, and tons, of these troops. When push comes to shove, though, if you are up one or two significant techs on your enemy, a decent stack can take out multiple of these armies per turn. Easily.

What you invariably notice is that killing a couple of these stacks hugely shrinks the AI power meter, so that a computer that appears to hopelessly outgun you can start looking like a well-matched opponent a couple of turns into  a war. This strongly suggests that the faction power meter is weighted too heavily to the number of troops a faction has on the ground, and not enough on how powerful or resilient those units are, not to mention the capacity of the empire in question to sustain a war effort.

Second, what is a viable strategy if you *are* resigned to spamming tier-1 units? If you send them all at the same stack or target, that might be a viable option. And to be fair, the AI does seem to be doing that. It does not, however, seem capable of changing its target once the horde gets moving. For instance, if it runs into a stack of mine, the AI army basically attempts to move by without engaging it. Of course, to defend my city, I attack the enemy in the field. This lets me chip away at the AI army at my own pacing withougt the AI really using its one advantage-- more units.