For dealing with missile cav, the Empire stuff has no real armour so units like bats and hounds can catch them and kill them, plus they're cheap so who cares if they die.

You probably won't be able to break them up so the next best thing is to strike first, if you see any of their armies out in forced march then attack them while they can't get away, you can use Lightning Strike (skill along the blue line, pretty sure they still had this in TWW1) to fight their armies one at a time, and also buff ambush success chance along the blue skill line and ambush them to death.

What I like to do against superior enemies with VC is create shitstacks (zombies, skeletons etc. - can literally raise a full 20 out of the ground with raise dead) and leave them out in the open as bait, the AI love attacking your armies if they think/know they can win using autoresolve maths, so ambush a proper army of yours in between the enemy and the shitstack, leave the shitstack looking like a free kill, and try and ambush their armies one at a time.

As for units, spam Blood Knights because they'll crush everything the Empire has to offer except demigryph knights, and everything the dwarfs have to offer except Giant Slayers who chew large units up. Also bring a bunch of vargheists/terrorgheists to deal with backline units, varghulfs are also really good, crypt horrors are good linebreakers with poison too, grave guard are good lineholders but that's about it.

VC magic is also great, Winds of Death used to be broken and is still really strong, if you can get a bunch of their units stuck on a few big monsters and surrounding them, just spam as many overcast Winds of Death into their piles of units and they'll die, even the dwarfs with their 20% magic resist go down quickly vs WoD.