Having mass Flyrant is going to beat a straight
TWC list. It is the only aspect that they are weak against. That being said, you have enough high toughness squads to run around with, you can play out the mission and do well.
A couple of Flyrants aren't too bad. He'll have a larger ground presence at that point. Charge big things and stay in
CC. Then he's wasting 450+ points.
CC Carnifexes are trash vs
TWC. 4s to hit 2s to wound and
SS still gives you a 3+ save no matter what, AND you have two wounds that they can't double out without crushing claws. Dakka fexes are like flyrants, except you charge them and they disappear.
The solution to the mass Flyrants isn't going to be perfect with a true
TWC army. Too many points are sunk into the ground game, and I haven't seen any reliable space marine counter to 5 flyrants. Wolfguard in a pod will help (turn one you can kill a tyrant outright if you get first turn). Better would be sternguard in droppods because they have the poison bolters after the combi melta is used that will cause issues for the flyrant.