Not entirely true, although I will admit changing coil springs is a much cheaper and easier exercise.

Up front, changing ride heights, whether torsion bar or coil over, will net similar results in geometric changes. Altering pick up points between an aftermarket tubular coil over system or the OEM torsion bar system is not done easily, although...by retaining the original mopar parts, you can swap to taller spindles (FJM or C body) and taller ball joints (offered by several oval track parts suppliers) to alter intersection points, and ultimately, roll center locations. None of the aftermarket systems I have seen allow these changes, use compatible parts to adjust spindle heights, nor offer control arm mounting point adjustments. But, a big drawback to the OEM system is that t-bars are expensive and you are limited to 4 maybe 5 decent rates, provided you match them up with big enough sway bars.

Out back with a stock leaf spring set up, no, you can't alter roll center easily. However, changing the front eyes to pivot style eyes and adding an adjustable panhard bar will now allow easy changes in roll center height for a live axle set up. However, quick rate changes with leaf springs is not easily accomplished.

FWIW, the original AAR and TA race programs used both watts and panhards with leaf systems when racing the TA series in 1970. Plymouth had panhard bars and Dodge used Watts links. As Plymouth was qualifying better, the Dodge team elected to dump the watts for panhards and improved their qualifying positions.

Now, that isn't intended to say a watts in ineffective, as they have been used successfully in many applications. However, what it does tell me is that in a competition environment, sometimes the simplest solution is more effective in application than the ultimate solution.