This, and the other thread, make the mistake of assuming that the mobs in DDO are anything similar to the player characters. Mobs do not have gear, they have stats.
That said, there should never be a time where a character’s special attack should be completely useless. This was one of the better parts of the changes to Smiting/Disruption/Vorpal a couple years ago. They may not be able to insta kill bosses, but they do add enough damage to make them worthwhile in fights against bosses. It’s too bad that the current crop of developers had to undo this with the current crop of weapon damage mods.