[pluma]

I think "useless" in this case is meant in the sense of "isn't used much". The Ruby community and ecosystem is dominated by Rails to a much greater degree than Python is dominated by Django.

Django is merely one of the more popular solutions to a larger niche of what Python is used for. The closest equivalent to Rails in Python in terms of dominance is probably SciPy and even that comparison is a stretch.

The Python ecosystem is much more diverse than Ruby. Not because Ruby can't be used for anything other than what Rails is used for, but because there are simply more people doing the different things Python can be used for.

And ultimately the practical usefulness of a language depends not just on the suitability of the language itself for the given task but also on the availability of libraries for the common problems you encounter when solving that task. So the usefulness of a language (for a given task) is at least partially defined by how much it is actually used (to solve that task).