workers could just as easily jointly work for themselves in a non-capitalist setup with investors still being compensated.

They can do exactly that in a capitalist system, it’s called a worker coop and those do exist.

To sell labor, there must be a transfer of responsibility, but such a procedure is impossible

What do you mean? When you work for a company, the company takes responsibility for any mistakes you make. If you make a faulty product, customers will sue the company, not you. If you get injured on the job, the company must pay for your recovery. That’s the whole point of a corporate structure.