I think what’s needed is the introduction of additional pieces.

1. Pikemen - can’t move, but must face in a specific direction. Can attack any unit in front of them, but not to their sides/rear.
2. Archers - can attack any unit at least two but no more than 3 spaces ahead of them.
3. Trebuchets - similar to archers but can only attack 5-6 spaces ahead. Trebuchets can take out rooks.
4. Knights can kill bishops, but only at the hinting request of the king. The bishops can then get a free attack on the king, but can only whip him and not kill him.