Eyg

[Ghost of Rom]

I thought the idea was that AP bonus is supposed to negate armour bonus but someone with no armour should get sliced up like a good un?

The armor piercing bonus only applies to armor. You can still have a good defense value without armor by adding valor.
The axe men have a standard attak value...say 5. Plus if the enemy is wearing armor they receive a bonus depending on how good the armor is. Higher armor number bigger bonus. So if you have say a unit at armor 9 you may be getting a bonus of 3 or 4 added to the standard attak value of 5. Now the axemen are attaking at 8 or 9. Better to have a low or no armor unit on the armor piercers and put your armored troops against something less lethal if possible.