They are fine if you compare them with Doom Armors & Illusions!
Seriously speaking, I think it's part of the difficulty to get less XP (since some monsters are better left alone). And they could still be cleaned up without much resources: prep bear mace and JJ (for WEYTWUT) and you can smash other monsters into them. PISORF shine there too. It's just a matter of how much you value XP.
Doom Armors and Illusions are sort of limited in where you can find them. Illusions are more of a terrain gimmick than proper monsters, really, and Doom Armors are cheezy AA's (which is sort of perverse when you think about it).
And I think it's a bit more complicated than that. Yes, they work exactly like that, they reduce the ammount of "easy" (hmmmm, not sure if anything but Gorgons, Goats and Bandits are "easy") XP, but in plenty of Vicious runs there is allready very little Easy XP to go around anyway.
The prime offender, erm, example here is Dragon Isles IMO. High lvl Zombies and High lvl Meatmen have always been "not worth the effort" roadblocks in my eyes, and if you add Goo Blobs, you have 3 guy's that are quite difficult to tackle if you need to conserve resources. And then they stick AA's in there. (haven't played it in a while, but it used to be this way). Sure, you have the dragons you need to fight, and all that, but still, that's hell of a lot of fat right there. It makes you have to fight a lvl 10 high magic DMG boss at a really low level, which then requires you to be able to do that (skill wise and game mechanic wise). That means that compared to that level, any level that doesn't have Zombies/MM/Goo/AA's/Boss Dragons will be a cakewallk for anything that uses the same strat. Widens the gap so to speak, and by a good margin.
And aestethicaly, the damn AA's stick out like a sore thumb, I mean, they fit some places thematicaly, sure, but not everywhere. What's the list of dungeons you can find them in? Dragon Isles (aestethic WTF), Daemonic Library (stretching it, but not as bad as Dragon Isles), Halls of Steel (obvious fit), where else are they? Maybe they're not even so common as I thought, but whenever I see them outside of Halls of Steel I sort of feel -.-
Not sure what was the intention behing making them so fat and seemingly ubiquitus, but I'm sure VICIOUS could still be VICIOUS as oposed to HARD without resorting to sneeking in a "stealth" boss as a monster type.