Ambushes aren't fukking war fare strategy, just lazy as fukk writing (and a device that's been used in almost every single major GoT battle to date). Do you think they didn't have scouts in medieval times?
Have you not read The Art of War? 33 Strategies of War? Kingdom???
Yeah, they would have large scale battles but maneuvering and counters are crucial to winning battles, not just throwing bodies at the enemy.