Melee guards right now seem to really take a considerable amount of time to decide whether or not they should swing their sword, keeping their distance and making themselves easy pickings for mobs that shoot, and when they DO make their swing they end up trading blows with other melee mobs anyway, including zombies.
And crossbow guards also aim and shoot a little TOO high. This causes them to struggle with picking off mobs that are more than 5-6 blocks away from them. They also seem to have a hard time loading their crossbows when they have food in their offhand, constantly swapping between loading it midway and taking a chomp out of their meal, even when they still have full health.
It also looks like the guards have lost their bow AI, since they still act as melee guards when given bows and a stack of arrows.