Yep, that's Tailoring. I'd rather see a player cheat, than tailor an armylist to beat me.
If you're having difficulty with Balthazar, I have 2 suggestions which can be used together at the same time -
1. Lore of Heavens - I used this on a Vampire sitting on top of a Dragon once, and it was hilarious. Two of the spells cause D6 S6 hits (chain lightning isn't just for packed armies) and the lore attribute causes an additional D6 S4 hits to flying models. When you slam someone with 2D6S6 + 2D6S4 hits in a single phase, they usually fall right over.
2. Daemon Prince - he can fly, and he doesn't wear any armor. Plus he can go with MoT for a 4+ wardsave (if you don't run him as your Heavens guy). The thing about him flying though, is that he can hang out behind your lines and wait to get the drop on Baltha-sack. If that pegasus riding pansy comes near enough to cast a spell, you hop over your guys and eat his face with the Daemon. A Disced-up character can do this too, but then you're getting into armor, and even our basic 4+ makes Lore of Metal a bit scary.
I wouldn't take Wulfrik against him though - he's not in a unit, so you don't need to challenge him out, and he flies, so he'll avoid close combat anyways. I'd still take Wulfy to deal with his gunline (because he sounds like that kind of a guy) but I wouldn't chase Balthazar around with him.
If you want to counter-tailor a list to fight empire, hordes of Marauders paired up with flying characters (move a unit, fly the character to it, move the unit he just left, repeat - it keeps your Discs in cover without slowing your army down) and some nice Leadership spells will wreck him. Heck, your Marauders don't even need Greatweapons against Empire - you already wound him on a 4+ and you're going to mulch his lines when you all strike simultaneously.
But that's not the point. Tailoring an armylist is the point. If you can, swap armies with a friend, and beat this joker. If you're playing with a local group, have everyone write one armylist to use for the week, and draw straws for who plays against eachother. Or put all of your armies into a collective "pool" and just share. My group did this for a long time, and I can honestly say that I'm now comfortable picking up any armybook in the game and writing a competitive list with it (it helps that I own half of the armies already). Learning and playing with the other books will give you a better understanding of the game anyways.