I don't really mind fights requiring different party makeups to some extent. More variability would be neat in some cases. I like warriors in strength stuff as pseudo-dps (it'd be neat if the officially enabled it with mixed str/vit accessory drops in addition to the super expensive crafted stuff). I think it'd be neat to have coil fights that work best with 3 tanks or whatever.

People want to get things done quickly so they try to squeeze in more DPS. Plus there's the fairly strict DPS checks in place along the line so moar DPS is pretty ingrained. Problem with tanking is that it has to be a damage level that's set for the minimum ilevel because it's something you can't really game.