The empire greatswords aren't that terrible. The length and shape is mostly right (I've got one that goes to about my chin, so 1.70 I guess). The issue is that the handle is too short. With a greatsword, a third or more of the entire length is just the grip, so you can use leverage to get it moving. Of course, Chaos is also overly spikey, but that goes for all their stuff.
Double-headed, huge axes (looking at you Grimnir/Gotrek/Borek) are much more unrealistic, because all that metal creates a huge cost and makes it a total bitch to swing, and tires you out. The huge hammers have the same issue. And that's also the reason why buster swords are dumb. Of course, when you get into magic and superhuman abilities, design considerations change.