I don't autoresolve my siege assault battles but I don't "assault", either, I siege until the enemy sallies or surrenders. It's one of them, or nothing, as the assualts are so dull and every single one is almost the same- there's no grand sweeping movements, no manouever, no room for strategy beyond "make another hole behind them". And there are way too many of them, that's why I still play with the big map mod, simply so I can play open field battles more often.