The pilot reported that after landing, he moved the throttle to idle; however, the engine speed remained at 1,550 rpm. After verifying that the throttle friction lock was fully released, he decided to move the mixture control to idle/cutoff to stop the engine. The airplane subsequently went off the end of the runway and impacted some bushes. The left wing separated at the wing root during the impact sequence. He noted that a throttle linkage issue may have prevented the engine from reducing to idle power. An examination conducted by a Federal Aviation Administration inspector confirmed throttle control continuity from the cockpit to the fuel servo, and that the fuel servo throttle arm rotated smoothly from stop to stop. Additionally, the left and right wheel brakes appeared to be leaking, and the pads were worn below minimums. In a supplemental statement, the pilot noted that the brakes were functional but required more pressure than normal. He added that there was no issue holding the airplane in place during the before takeoff engine runup. The airplane pilot operating handbook (POH) specified an engine speed of 1,900 – 2,000 rpm for the before takeoff engine runup. Automatic Dependent Surveillance – Broadcast (ADS-B) data depicted the airplane approaching to land on an extended final. The final data point was located about 0.5 miles from the runway. At that time, the airplane groundspeed was about 108 knots. Additionally, a left quartering tailwind prevailed which provided a 3-knot tailwind component to the landing runway. The airplane POH specified a final approach airspeed of 71 knots. There was no evidence of an anomaly with respect to the throttle linkage. However, there was evidence that the wheel brakes were likely not performing at an optimal level. The brakes in combination with the airplane inertia during landing likely resulted in the runway excursion.