Are Shields Worthless against AN Attacks

[shatner]

If you are facing something that does AN damage, about the only thing you can do to prevent that damage (barring elemental immunity) is to not get hit. If the attack is ranged, a shield might help, with the bigger the parry bonus the better. However, if it is a melee attack, does a shield do any good?

Normally you would want as high a defense as possible to prevent getting shanked by a duskdagger, for example. Well, a blacksteel kite shield raises your defense nicely. However, if the attack would have hit if it weren't for the shield, my understanding is that the hit still lands but you get to add your shields considerable protection to your own. Which is great against anything except an armor-negating attack. In fact, since most shields offer a defense penalty, you are actually making yourself more vulnerable to AN melee attacks by equipping them.

Am I interpreting this correctly?

I ask because I had my pretender fight a dream horror once and he was horror marked and diseased as a result of the battle, despite a very considerable amount of defense. Now the easiest explanation there is just bad luck but I wanted to see if I was worsening my luck by bringing a towershield to the fight.