It's important to keep in mind all the things that factor into the power rating. I don't have the link but there is a article on these stats which can be found in the War Academy.
AIs power rating is often very much skewed by factors other than units. Although high unitprob AIs like Monty and Shaka tend to have tons of outdated units. (Actually, when it comes to high unitprob AIs, I would worry more about Nappy and Mehmed, especially Nappy, as they tend to have a better economy and, hence, better units).
Other factors are buildings like walls, castles, barracks, stables and the Herioc Epic. The AI spams most of these buildings when they are available. Obviously, walls are generally not a big priority, except maybe on border cities to nast AIs. However, HE should be a priority as well as a few high prod cities with barracks and maybe stables. This will help your power rating some.
To me though, the important thing is the quality of units, a military tech advantage of some aspect (Curs , Rifles or Cannons) and the ability to produce these units rather quickly when needed - high hammer cities, HE, and high food for draft. In this case, you don't necessarily need to spam tons of units. Build enough and make sure you keep larger stack on your border cities to avoid surprise attacks.
As for power rating, try to be in the top half of the graph and definitely not the lowest, although you most likely will be for a brief period in the early game since AIs will have lots of archers while you have warriors.
You don't have to be number 1 in power but having a good power rating does help ward off attacks so you can pursue more peaceful objectives. It also provides some diplo bonuses and the possibility of peace vassaling peaceful civs.