The sole purpose of that curved bar is to strengthen the connection to the diff. So long as the third link is strong, its tension or compression is moot. The downside of a torque arm is a tendency to brake hop, which is very bad in autocross. A tri-link can still get brake hop, and in RX-7s it was solved by using a section of pool noodle as the bushing in the front mount of the third link. So much clanking and banging that it wasn't streetable, but they stuck like glue. My RX-7 had the factory 4-link/watts, and a competitor had a tri-link/panhard suspension. My car handled good to a point, but then would breakaway and slide. No matter where he turned his steering wheel the car just went that direction. It was an amazing difference.