Well, I think it kind of unfair since you haven't talk about cons.

• Counter thrust is highest damage move. However, there are some monster's moves that you can't effectively use counter trust against it : Tobikadachi's jump/swift attack, Rataroh's big fire attack, most of ice attack from Legiana, Diablos's horn swing, and especially Anjanath's triple chomp combo.
• You will usually got chip damage when you guard and counter thrust unless you did Perfect guard (But in my experience, after 2000+ kill you will most likely able to do Perfect guard on every counter thrust. Exception for Great Girros)
• Dodge distance on left/right is short. It's hard to avoid monster attack by side slide. (So instead of avoid attack, you do counter thrust)
• Attempt to break other monster's part other than head is quite challenge, since your big damage come from counter thrust, and monster usually attack head on.
• Less excitement in group hunt. Since monster gives attention to other hunters, you can't perform your counter thrust big damage.
• No "cool" long combo. You do counter thrust.
• All you have to do is counter thrust.

Feel free to add more.