If you separate revenue and control (employees get to vote on decisions, but investors get the revenue), then employees will be incentivized to maintain the status quo instead making decisions to make the company successful. The employees have almost no incentive to make difficult decisions like cutting unsuccessful lines of business etc. I would be very uneasy about investing anyone's retirement savings into such an organization.
If you keep revenue and control combined (a simple share structure, where each share gets a piece of the revenue and a vote, and employees get shares when they join), then you have other paradoxes. To make this work, you need to prohibit employees from selling their shares to investors, otherwise you're back to a conventional corporation. You also need to take the shares away from employees when they leave the company, otherwise former employees become a de facto investor class that you wanted to avoid. As an employee, I would prefer to work at a company where my equity does not have these restrictions placed on it.
You may say "but if we all just tried a little harder to believe in a better world it could be possible". But it is possible now. Cooperatives work easily under existing corporate law, and are even incentivized in some places. They just aren't very successful for the reasons above. The only widespread form of cooperative is doctor's and lawyer's practices, which are legally required to be organized as cooperatives through a limited liability partnership structure.
To make cooperatives work in the broader marketplace, you'd have to force employees to accept restrictions on their equity or force savers to put their money into cooperatives managed by employees who are not incentivized to invest it well.