And the reason that Wraithguard have pretty much taken that role is that the cost increase of Fire Dragons has massively swayed the balance between them; Fire Dragons used to be roughly half the cost of Wraithguard, but now they're about 2/3 the cost and still have to be closer to really screw vehicles up.
The extra toughness that Wraithguard offer as an alternative pretty solidly wins them the role, that and they can be Troops.
Sort if makes me happy. I have a set of 5 metal ones and while I sort of liked them in 5th I went with dragons far more often. Looking forward to having another excuse to drop them into a list.