Well I've played only a few scenarios vs the AI all the way through. About 90+% of my play is player vs. player. I'm just not into playing the AI.
For larger scenarios I'm not even considering Player vs. AI at all actually. I'm thinking player vs. player only and my remarks are from within that context. I figure if you can make that work, then *maybe* you can think about AI scripts if that's what floats your boat. Where it would become a time sink is if you got into connected battles ala Red Barricades in ASL where the prior day's results had an effect on the next day of battle. Because there is no forwarding of data and interpretation of that in the current game system, the designer would have to design a specific scenario for every conceivable outcome of that day for the next pulse of operations lol. Which would be exponentially more work.
There is AI in pbem too but only in the sense that it's reactionary and thus not scriptable in the scenario builder: the AI only reacts to a player's move (Btw, in this regard I think the AI would probably work just fine in larger scenarios).