This is the malaise that come with Xara introducing new features with scant regard for the consequences and the prior tool that is made obsolescent.
Most would think that replacing the soft-grouping capability with Live Copies would be the professional thing to but but Xara just fragments its products so that Live Copies can only be created in XDPX & XPDG but used in all.

As you advise Live Copies cannot be used in the same fashion as Soft Groups so we are stuck with two half-baked features.

Acorn