" What's stopping you from replacing the investors/managers? "

You are unclear.

How could "you", an employee, replace the investors/managers? "You" are a lowly employee with no power.

If you mean in a coop, then everyone in the coop decides when they replace the manager or whatever. They also decide how much everyone is paid and how much of the profits are saved within the company and/or invested in their futures, healthcare, the community, intern programs, advertising, etc etc etc.

If you meant something else then I didn't catch it.

" The entire collectivist system intentionally keeps unemployment high... "

"Collectivist system"?

When times get tough, a capitalist corporation would lay off people to cut costs, save on benefits, and make the others work harder - forcing the laid off people to go on welfare (externalizing the expenses back onto the government/tax payers), suffer, find other work, become criminals, etc. Meanwhile the profits remain in the hands of the few. The corporations might even cut corners and pollute the environment.

When times get tough, a worker coop would reduce everyone's hours, protect the jobs thereby protecting the community, and manage their resources and savings to get through. A coop would never poison their own community. Collectively they could take the hit easier than a few victims of a layoff that then become community burdens.