Looks on the TF109 may be subjective, but you cannot judge a sharkfin's usefulness "because others won without it". Formula 1 cars are complex aerodynamic structures (especially last year's hyper-aero cars), and McLaren's car happened to work well without one. By the same token, I could claim bridge-wings and horns aren't beneficial because Ferrari won the constructor's championship without them. There's great benefit in the fins as far as aerodynamic stability is concerned: Under jaw, it helps stabilize airflow and return the car into line, and even when not, flow-separation between the left and right halves of the engine-cover helps smoother airflow hit the rear wing.