Myphsar:
the slowness isn't an issue for a number of things in Doom, if you have the requisite Tactics and mana pool to use the Armor Ignore special a lot. The Renderers, impalers and Knights are especially vulnerable to being hit by Armor Ignore, while it only makes the DF mad, and the other room bosses have low enough resists to where a faster weapon will do you better.
Even if only 1 in three attacks is an AI, you'll probably get comparable (if not superior) DPS to a faster weapon without using special moves.