How are people leveling DoH, by the way? It seems super slow to me but maybe I'm doing it wrong.
It's not slow at all, it just feels that way.
Once you get past the level 5 nodes you should be getting 100+ exp(more as you get to higher level nodes) per hit, so over 500 exp per node.
From level 4-15 make sure you use Sharp Vision I (or the BTN equivalent). Also do not go for high level items. Go for items that have a base success of 90% or higher before vision buffs are applied.
Once you get to 15 try to aim for the highest item with a 90%-100% success rate and use Unearth to get HQ which triples your exp for that hit. At that point you will also have whisper buffs active from nodes, so try to use Unearth on nodes that will give you +1 attempt or +10% success rate. Use any others to build up your GP so you can use Unearth on the good nodes again.
There is probably a whole lot more, but I'm about to eat dinner. If you're on Ultros shoot me a tell (Bellona Hecate) if you need some help with DoH stuff.
Past level 15 it stays the same. I have actually ran some numbers on Unearth II vs Unearth I, but depends on it's GP cost (for Unearth II) and whisper buffs of the nodes in the area. I'll probably take a look when I get back on, since I have not looked at it yet.