To up the ante a bit more, I decided to increase the size of all enemies, including orcs. For the most part I just x3 or added 15 or so onto it.
As such, when building up my military a small group of 8 goblins ambushed me. Size 21 goblins. I thought "Eh, this'll be fine" and sent a group of 4 champions at them. Each of said champions could probably wipe out a small army of regular goblins. 5 seconds later, all 4 champions were dead. The goblins were already inside the fort, and headed straight for the mass of civilians in the main meeting hall.
Naturally, I decided to go out in a blaze of glory, and activated all 70 military-capable dwarfs, and sent the remaining 4 champions towards the goblins.
The dwarves piled onto the gobbos, mostly just punching them or trying to wrestle them to death.
As you might think, since 4 superdwarf champions (legendary wrestler + another weapon) were killed immediately, this civilian militia was somewhat short lived.
In the space of 10 minutes, all but 9 of my dwarfs were dead, and those remaining were either dying or traumatized. They managed to take down 3 gobbos. And it was glorious.
Having spent 4 years building up this fort, nursing it and caring for the inhabitants, I decided to quit and savescum. Now 6 months on from that now non-existent encounter, a force of 16 Orcs have appeared, most of them armed to the teeth, each of them standing at a towering size 32. Which puts them bigger vanilla megabeasts. As such, I am currently employing a cunning tactic. Hiding and hoping they leave soon.
Maybe after another year or so of training my growing army will be able to hold their own against them. Maybe.
Tl;dr, Orcs be awesome, their punches make my guys asplode atm.