"As I see it, how much compensation owners of capital receive is an empirical question, and the answers vary by different social settings. In the US, for example, employees who manage capital owned by others (e.g.stock brokers, corporate executives, etc) receive much higher compensation than the actual owners of that capital (e.g. retirees or savers). Your theory does not seem to be able to explain those empirical variations."
You are conflating "owners of capital" with "capitalists."
The ownership of capital by pensioners/savers is divorced from any form of control. All it has done is to establish a continuous flow of money into stocks/bonds, allowing capitalists to extract further rents through fees and ever more complex financial products. The other thing it has done is to further convince people that the interests of workers is aligned with the interests of capitalists.
Joanna