When breaking windmills without a wrench, a machine block is dropped. However, the windmill recipe gives two windmills per machine block, so you're effectively gaining 4 iron every time if you craft and then break windmills.

I like the carbon plates recipe, it forces you to get some basic infrastructure set up (compressor and a generator) and balances it a little better too.

Humm, I think the easiest way to fix this is to just make them drop themselves

Windmills should be crafted like this normally so they should effectively drop a machine block.
The easiest fix is to change the recipe!

One generator and 4 carbon plates!

Thanks!