Not many new track smooth roads around here but even on a good road the Mustang can’t corner well. Maybe it’s not just the rear axle... maybe Ford just doesn’t know how to engineer good handling.
Well, the old SN95 and earlier Mustangs with stick axles sucked. The 03-04 Cobras with the IRS and the blower handle very well, especially if you do a bushing replacement and add full-length subframe connectors.
The S197 with the stick axle isn’t nearly as bad as the SN95 and Fox Mustangs were... but it’s still not great.