Not always.
Harrier pilots used their thrust vectoring to good effect in dogfights.
Getting whomever's on your tail to overshoot and present their 6 o'clock to you is quite useful.
You can do that with speed brakes, thrust vectoring, unbalanced (non-stable) fly-by-wire flight controls, you name it.
Obviously, preventing an aggressor from getting into firing position would be the best solution, but if you're already in a pinch, it's nice to have a Plan B.
You're limited by how many G's the pilot can endure in the violent maneuver, but it's already part of the training for our folks in the cockpit.