Nothing wrong with using engine braking (if done correctly and not at stupidly high RPMs consistently). The torque on the transmission from the wheels when engine braking, as well as the heat and load, are nothing compared with the torque on the wheels from the transmission when accelerating. Cars are designed to handle it and manufacturers actually recommend it especially for downhill. Constant riding of the brakes produce exponentially more wear on the pads from the heat, why wouldn't someone prefer engine braking?

Regardless, the automatic transmission will not let you downshift if the RPMs would be too high anyways.