Well, the way I see it, I would win most of the battles anyway, but just don't have the time to do it more than half the time (that would be defence) as framerates in sieges are abysmal, and they make playing assaults feel like driving a hot nail through my temple. I got so tired with the endless siege battles in Rome, so why not? it's after all meant to be fun and not feel like trying to dig a well with a plastic toy shovel, having to fight through 2 rings of defence while the framerates go down to new lows and the enemy doesn't really know how to defend itself. Defences are a bit more fun as they can be dealt with so that the framerates stay at decent level (by not looking towards the city/castle).

The same goes with pre-1.2 inquisitor smashing with 8 military units. Perhaps I just like cheesecake more than dry bread with nails baked into it. It's a fun game, but I still prefer the field battles.