[Sombre]

Skaven have serious problems versus Tomb Kings. They have poison and disease immunity, excellent massed missile fire, swarms of chaff,.. all the tools needed to whomp the poor ratties.

I don't think giant rats make good chaff against archers. They die too easy and run too easy. Clanrats with sermon of courage would probably be better. But Skaven don't really have much of a counter to massed composite bows, longbows and whatnot.