XV did road course test a fully restored, all original TA to create the baseline that they are using for comparison of their system gains. If anyone has followed the XV series on Dreamcar garage, or done any research into suspension sytems, you would know that the GEOMETRY of a stock Mopar is actually pretty good. The spring and shock rates certainly need to be improved upon to make them more comparable to a modern car. Once that change is done, then yes, they do perform quite well, even in big block form, compared to a modern car.
Comparable to a modern performance car, well, sorta. Ultimately road holding ability is about a cars balance, tires, spring, and shock rates. Match these items car to car, and a E body is right in the fight, but stock to stock, not a chance. Remember the physics of holding a corner do not care if you have leaf springs or coil overs, aluminum spindles or iron.
If you go back in the day, Mustangs, Camaro, and Javelins did win more championships than the Mopars, if for no other reason than their duration in the series and the factory commitment to the teams. Chrysler only official participated in Trans Am for one year. In that year the Mopars qualified up front regularly, but engine and transmission failures usually resulted in DNF, which will kill chamionship potential.
If you ever get a chance to look under the original TA race cars, they are much more trick than just leaf springs and torsion bars. Everything is adjustable. There are adjustable sway bars and even panhard bars to change roll center location in the rear, which is rarely seen on a leaf spring suspension. Also, while not available today, they used gun drilled torsion bars with variable indexing anchors from the Nascar program. Some of these bars came in HUGE sizes of up to 1.8 inches across (1.22 is the biggest you can stick in a stock anchor, BTW).