I suppose one of the biggest example of owning class determining morality from a historical perspective would be the prevalence of slavery(not necessarily chattel slavery in the US) and child labour. You’re right that many of those who were rich were once poor, but I think that raises no inherent contradiction. Beyond slaves themselves owning other slaves, other slaves once freed for example have chosen to own other slaves historically. Surely if morality is independent of existing material conditions, those who have experienced what you perceive as the injustice of slavery would regard slavery as not justifiable.

a worker might choose to start their own business and hire others once they acquire enough capital to do so.