Earlier quoted context omitted.
Moving money from rich people to people much more likely to spend it rather than hoard it should result in a significant GDP boost.
You misunderstand the fundamental mechanism for improving standard of living: productivity gains. Consumer spending does not improve productivity. Rather, investment in capital goods (by those rich hoarders) leads to productivity growth.
I'm not sure that "rich hoarders" have an appreciable positive impact on business investment in depreciable assets. Most capital assets are purchased to produce goods and services to meet demand, which might be stimulated more by redistribution.