I think the reasoning behind the AC/UAC damage discrepancy is to keep the DPS ratio at 2:1. UACs fire twice as fast but have to pause periodically to cool down, so individual shell damage is higher to compensate for this. It makes sense, depending on how you look at; UACs can potentially deal exactly twice the damage of standard ACs, but only if fired with optimal efficiency (no overheats or wasted cooldowns).
I am liking the AC10 in general now. The Warhammer B in particular can lay down some nice long steady barrages.