Agreed. Unlike a broadsword or a battle ax, a war hammer has less chance of slipping of a smooth surface like a shield. In the old days, people also grease their shields.
However, you need to be a big boy to do this to armour. Maybe I should go on a diet of haggis like the old days when the scottish were brave and wild.
But more seriously, why did the chinese use 2 hammers at once? I though you would like to weild it with both hands to make each blow really count. As you're not trying to hit the target but move it out of the way, hopefully into another opponent. very useful in a battle field when you want to clear space or break your enemy's formation.
It's not like using 2 broadswords that you're making use of the cutting edge.