How much is too much? I don't know, what I do know is that if I own a company I would pay the executives far less than they get paid. Why? Because they don't take the same risk as I do. Why doesn't this happen today? It's because shareholder's are passive investors and the manager's are able to skim off the top.
This is a classic case of dispersed costs, concentrated benefits. The manager's salary is huge, but as a fraction of earnings per share it is insignificant. When you have millions of shareholders they don't notice a fraction of a penny here and there. The manager notices all those pennies and therefore attempts to pad his compensation. Nothing wrong with the manager, doing exactly what any other sane person would do. This is not good for the company.
The solution is more concentrated ownership in companies. These people would feel all those pennies being siphoned away and would put a stop to it. Is there a cost? Yes, reduced capital formation. I think this is a beneficial trade off.