The heavier the weapon, the slower the swing. Heavier weapons confer more energy and are more likely to cause internal trauma even while wearing heavy armour.
As k/t said you should balance with a high attack stat, combined with a large attack delay.
Currently these weapons are only devastating to armoured units, while unarmoured ones should get punished as hard. However due to unwieldy weapons these units should suffer themselves, especially against agile, fast and lightly armoured 1-handers.
Back to topic:
2-handers seem quite inefficient. They perform best when combined with a meatshield. Let them attack through your low tier units so they add killing power but don't get surrounded and staggered.