[HoneyBadger]

I agree with you, PvK-large shields and huge morning-stars are poor choices for fighting underwater. However, the spear and buckler combo is just as poor on land, for the Agarthans. I guess a solution would be to create some units who fight with weaponry suitable for land-based combat, and others for water-based combat. It's too bad they can't simply drop one weapon and pick another weapon up, though.

If I had to arm Agarthans for amphibious combat, I'd definitely go with a 5 pointed trident-weapon (four short, sharp points about 6 inches apart, surrounding a central spike or blade) and a weighted net. The buckler would definitely go, it's mostly just dead weight, underwater.