Ooh, that's a good idea. I'd have to set a few things specifically for testing, but this could be a big help.
The changing statues aren't intentional. I think I know the source of the issue, though.
Avarice Fiends do count as Shadow-based for Holy Water damage calculation. The issue is, the effect multiplies the final damage, similar to Amps; since Avarice Fiends have a lot of Defense, you might still end up doing very little damage if you don't have a lot of Attack. Maybe I should alter the formula a bit... I'll have that and the bridge fix out in the next patch.