Here's a quote from the above link.
The most common casting rotation is this: IS/SFx4
The highest DPS casting rotation is this: IS/MF/Wx6
Well, exactly. For DPS, you Wrath, and that's where Nature's Wrath gear comes in.
Here's what the question reduces down to for me:
Why all the bias for mana efficiency when you'll often, depending on instance, bring down trash mobs before that's an issue? IS + SF might be good boss material, but it makes you inefficient against trash.
My guess is that the only way +nature dmg gear hurts you is if you...
1. Run into nature resistant mobs.
2. Are forced to back-up heal mid-fight.
3. Have a fight that lasts longer than you have mana.
The first would stink, but I haven't seen much of this outside of Nagraand. The second happens. You can swap idol and weapon to help, but yes, if your party starts to go down around trash mobs, you're in trouble in more ways than just gear. The third happens, but usually the fight's under control by then.
For bosses, you *change gear* if you've got it, but I'd like to see the pre-instance reward gear that'll beat what we've got here.
I mean, seriously, I haven't quite put in the time to have Tiered gear like the examples from the forum post I linked in the first paragraph: Madrox, Caliane, Skeldi, and Horao. Of course I'd rather have that stuff!