Not sure how you were able to kill Hai bodyguards with archery, their armor should have been too tough for that. Ptolemy FM are less heavily armored than Hai, but still too much to be worth shooting at with arrows (slings work very well, though ); I'd say reserve him for your own FM.

As others have said, you have to shoot phalanxes and other decently armored infantry from the rear or right flank. Spread out your HA, and one group or another should always have a good shot. The enemy slingers will be your only real danger; other than that I think you're correct in expecting an easy Heroic Victory.

Nothing wrong with relying on the basic HA model. It's also worth having a few tougher units in addition to your FM to handle melee duties. The various flavors of steppe nobles all look good for that role.