I disagree Ballerhans.

If you have poison resist potion (and i you are in the swamp you should always have one running) then the swamp is not "terribly unbalanced" as you put it ( my opinion).

Killing a lox in leather at range, as dumb as they are isn't unbalanced. Try melee range w/ a lox (or two or three) then have a couple Fulings come from behind a rock with a few deathsqueeters added for flavor. Plains can be rough.

Plains makes Swamp look like a cake walk (which is appropriate since Plains are 2 biomes after swamp).

Iron isn't hard to mine. They've made it much easier. Mud piles just break apart now. You can also use a wishbone in the swamp and find mudpiles outside of crypts.

I don't see anything unbroken or unbalanced about Iron vs dark metal at all.