Demons..basically ignore the existence of Damage Reflect.

Basically what Dark Link said.

Mihile is also an NPC so it's hard not to remember the class exists. The problem with Demon Avenger is probably very little promotion from Nexon and Xenon being released not too long after. I also seem to remember Xenon being announced first for some reason, but I'm probably mistaken.

If I recall it correctly, it was because there was very mysterious info released over Xenon before Demon Avenger was released. I remember a dark silhouette of Xenon with a few lines of text, and then all of a sudden Demon Avenger, while everyone was still wondering about Xenon.