> In practice, the Party owned everything, and its high ranking members were effectively nobility.
The concept of nobility implies hereditary transfer of privileges, which was not the case in Soviet system. It was certainly easier for children of Party bureaucrats to get their own spot, but it was not guaranteed to them, they could lose it at any time, and "commoners" could get into the ranks (and it was not something exceptional).
So Party was the ruling elite class, but it was not an estate/caste, as nobility was in feudalism.
I'll agree they were not hereditary, but that was not the point. The point is that there was a privileged upper class minority ruling over the commoners, which completely goes against a basic communist principle, the classless society. They violated one of their fundamental principles.
The concept of nobility implies hereditary transfer of privileges, which was not the case in Soviet system. It was certainly easier for children of Party bureaucrats to get their own spot, but it was not guaranteed to them, they could lose it at any time, and "commoners" could get into the ranks (and it was not something exceptional).
So Party was the ruling elite class, but it was not an estate/caste, as nobility was in feudalism.