Assume, for a moment, that we had an AI that was sufficiently adept with tactical movement that you could, at best, achieve a 5:1 kill ratio. All other Deity bonuses are left unchanged. Against such an AI, you would definitely need to turtle, and turtle hard, at certain points in the game. There wasn't really a point during RB3 when you needed to do this. Some of the tactical situations were certainly dicey, but you were still able to maintain relatively steady expansion until the end. Instead, you would be more reliant on Barracks/Walls/Castles/Forges/Heroic Epic/etc to hold your ground. Oligarchy and the Honor tree look much more enticing. Instead of building settlers, you have fewer cities with larger populations. Libraries/Universities/PSchools would give a better return for the investment. Capturing a city from the AI becomes a much more expensive undertaking, and you need a strong reason (like a Wonder) to attempt it. It also means that some starts, like the RB3 one, would probably be unwinnable. Combined with tougher building choices, that would make me happy.