The Bighorn2 is a lightweight answer to the original Bighorn.
The ATV guys figured out pretty quick that all that weight was eating horsepower (times 4, in their case). The Bighorn2 addressed this and the original Bighorn remained in production to satisfy the needs of hunters, heavier 4x4s, etc.
I have ran both. both kicked butt when aired down. All of them will tend to climb themselves in corners due their less rounded profile.
Any chance that is what you're interpreting as stiffness? I currently run a Terracross and they all do it. Of the three that I have used I prefer the BH2.
The other possibility is that the stiff stock shock is reacting to the weight of the tire and spanking you in the butt. Are you running a stock shock and swingarm?