Again, the assumptions don't tell us anything meaningful. If, hypothetically, we did achieve post-scarcity and pushed out capitalism in doing so, so be it. If that were to happen and then "bad actors" took back control of the capital, returning us to capitalism, so be. These models don't have to be ever-present, they don't have feelings, they are only descriptions about the state of the world at a given moment in time. Whether or not these forces described are in play is irrelevant.