It’s might not strictly be a zero sum within a company (presumably it’s value goes up and down) and sure, a company can increase its value and we would typically expect that gain (or loss) to be sent to the owners of that company.
On the employee level it feels like it’s closer to zero sum though, and maybe that’s just a perception thing. While relative CEO pay has gone up over the years I guess you can’t necessarily disentangle whether that increase comes out of the pool of wages available to all employees or whether it’s coming out of the pool of money that could be going back to investors. I guess I should go see if economists have any papers on that