I thin this is a bad idea, for Orthus specifically. In my experience, Orthus is VASTLY more dangerous if he has 50-60 turns to build up XP in the wild before he goes all out attack. Back when Orthus rushed you as soon as he spawned, I never had any problem killing him with a single warrior defending a city, or two if I was unlucky. Now that he waits around before attacking... there are times when the only reason I can stop him at all is because he never promotes to March. If you want to make Orthus nasty, leave his current AI, and encourage him to promote to March. For the rest of the barbarians I think this is a great idea, mainly because it will stop them all hitting you at once, and will force you to actually bother to defend your borders in the first hundred turns.