Advantage: Defense

[Ardri]

But what about intercepting - is the AI more likely to intercept you in the GC compared to the RTI? The AI hardly ever intercepts my army heading toward their cities in RTI.

I cannot compare the two as I didn't play RTI past episode 1 when I got the game and currently in my French campaign in Europe I have simply shredded through he minor kingdoms all the way to Saxony without fighting a major power(major kingdoms have more armies and thus I believe would be more likely to intercept you), but I do think that when you come into range of 2 AI armies marching into their territory the two combined will intercept you (I believe this is the case, I can't remember for certain off the top of my head). However, if it is your army marching against the regional capital the army they have within will not intercept for the most part.

I believe that the AI tends to only intercept/attack your forces when it can go into battle with superior or nearly equivalent strength. Given that most garrisons are lowly militia, the AI tends to try and play defense in a siege rather than intercept and fight a field battle it knows it will lose. I guess you could say the AI would rather lose later than sooner. That is just my observation of the AI's behavior.