Basically a shield wall and a hoplite phalanx is not the same thing. The weaponry used also differs for the very same reason. Using a description of a shield wall to explain why hoplites did not use their weapons the way we think they do is nonsensical.
In a shield wall you do use shorter weapons. Axes and short sword and the likes are great for a shield wall.
Hoplites did mostly use overhand grip. In a hoplite phalanx formation it makes the best sense as you can lower yourself to the ground, and cover as much of your body as possible with your shield, while keep striking the at the enemy. But don't take my word for it! Most ancient depictions of hoplites in action show a overhand grip. I kind of think the discussion should end there.
There are exceptions to this rule, but they mostly depict single combat. I could also imaging an underhand grip would be the most effective against cavalry, but I don't have any sources and sincerely doubt the engine would support different formations for different types of enemy units.[/Q]
He does mention about vase painting in a later video. They are designed to sell the pot. e.g, if there was a vase made today, you would not study that to learn modern warfare. It looks better overarm, therefore, it'll sell. It's overarm cause it sells.