[Grimgor]

As far as I've read (somethingawful.com has a huge ongoing AAR where it is explained in detail, albeit for multiplayer) domkilling the entire map is a long and slow process. Furthermore, those who do it are blood-saccing nations and using overwhelming amounts of temples (possibly strategically placed Inquisitors). I am making guesses here, but it seems that while Juggernauts would no doubt help, they're not as good as Jade Knife-wielding sacrificers.

All that being said, everyone is constantly working against your own Dominion spread, which does mean that the spread only goes so fast. Furthermore, as they're only available late game, I think that makes them of situational use. Bring a ton of them with an immortal SC pretender and a blood-saccer who stops every now and then to build a temple and do his thing. That way, you'd have some assurance of fighting on your own dominion, letting you go nuts with bonus hp and your pretender is not going to die. However, them being late game, I think most human players would have the means of sniping them.