Wheel hubs at both ends of a torsion beam are directly connected along with a stabilizer bar. You cannot move one rear wheel up/down independently without directly affecting the other wheel. THAT is exactly what independent rear multi-link suspension solves, because it has two pivot points. One for each side. You don't need to spend more than 2 minutes under each car observing the geometry of it to come to same conclusion which I shared above.
Torsion beam setup is easier to manufacture, has less moving parts and is mostly maintenance free, but it also provides the feeling of less stability and grip.
Pros and cons of Independent multi-link are opposite to that of Torsion beam.