In maps I've both created and downloaded, the AI always has a grasp on defense (towers and such), but never comes out of its base to perform a counterattack. It also doesn't seem to replenish lost forces. How can I correct this?

Try set harder difficulties
Try use new Ai, example from: https://www.voobly.com/gamemods/mod/859/Ai-pack
Try give Ai a fair Rm-like start, some trees, bushes, gold and stone. Make it believe it's a normal game.
If you need Ai at scenarios, try use triggers to command it.

Most of the scenarios I do are RM/DM variations with all of the above. However, I'm not familiar enough with triggers to use any.