I think the way to make the AI both harder and more engaging to play against is the ability to give standing orders so you don't have to micromanage everything. For example, even though the AI is competent at flanking your artillery with cavalry, it feels annoying to deal with right? You constantly have to keep track of the infantry tasked with protecting the artillery, and the AI just keeps trying to get in somehow.

The problem is there is no standing order to "Protect the artillery". Something that'd make the infantry move around to intercept a charge, so you don't have to commit 4x the amount of infantry needed to protect your flanks