The difference between the guys using 3D specific rigs and guys using hunting setups (for competitive 3D) is typically (in my expericence) about 5 spots in the final scoring.
Can you shoot 3D and have a great time....and be "competitive"? Sure. Are you gonna be a perennial contender with a hunting rig? I don't think so. Not around here, anyways.
Competitive 3D and hunting are 2 different animals.
Do I know some guys who shoot their hunting rigs and win? Yep. Few and far between, though.