Note, there still can be special rare cases, where such a freedom is really needed.I'm calling you on this one: I say there are not, other than selling software. Back it up or drop it.A good example will be the license of Guile or license of the run-time units of the GNU Ada compiler.
So, if those things were under strait GPL, by your usefulness definition, they wouldn't be DFSG-free, because they don't grant the freedom to create proprietary works?