I just did a mission with my santi versus a npc Victory. I had long cannons and top deck carronades, so I got close to him immediately, my first broadside ripped through his armor (from ~50 meters).
Because we were sailing opposide directions he managed to pull some range from me, but I still unloaded my other broadside, which only did minimal damage (thus a few penetrations), from ~250 meters. Then I decided to get close, again to ~50 meters and started melting his armor, it only took me ~10 min to sink him.
So I agree with the admin, that at range the armor is too strong. However, from really close range I think it is fine.
ps. I would like to provide some links of images of the battle, but I cannot find any forum rules..