Ushabti Great Bows shred anything they fire against and a Casket of Souls can destroy blobs on infantry that are giving you troubles.
From infantry killing power to ranged damage to blob destroyers to monster slayers, you have a construct that can do anything you need your army to do. Not only do they all have incredible armour values, but you have a monster that can fill any role that you need it to. Tomb Kings have among some of the best monsters in the entire game.
Because you want to play not Egyptians and roll over everyone with chariots.You want to play an undead faction that is also blingy as fuck?.Do you want to play an undead faction which is not totally villainous?.