I'm confident that Artillery can be used well in regular combat, the trick is always going to be in how it's placed. I tend to think of catapults etc as very long range super armour piercing archers that can't move. A single artillery piece is unlikely to be much of an asset, but having 3 or 4 catapults target the leading unit of an army as it approaches can yield decent casulaties to the target and the untis following it. I'm looking forward to using the cannon type units for this, their extra range means a couple of extra volleys before the enemy gets close.

I'm actually looking forward to creating a tank style army with 4 artillery pieces, 3 units of the best archers I can get, preferably Longbows or (Pavise) Arbalesters, about 4-5 units of swords/axes and the remainder Cavalry inc. a mounted archer or two.

Basic strategy will be to pound them with overlapping waves if missile fire (artillery first, then long range AP arrows/bolts, then finally faster but short range regular archers for those that want to close for combat). Infanrty and Archers should be hammered by the ranged assault, and those that try to close for combat will face the Swords/Axes of the waiting troops. Cavalry will swing out to the flanks and attack onces forces have engaged, hopefully triggering a rout.