Partnerships can have employees that do not own the business so they are quite different from worker owned coops. Think law firms.
WOCs aren't communist per se, although the spirit is there. As for communism not working, I'll offer up Marinaleda, Spain as a counterargument - though it is still early days. One could just as easily offer up the United States as evidence that capitalism doesn't work. It depends on how one defines success I guess. All societies crumble to dust eventually.
Co-ops have only been tried on a limited scale - and many a global company based on the current corporate model has failed. But do WOCs need to work on a larger scale? Is there anything specific about a WOC that makes it inherently impossible to operate at a large scale? They can still delegate decision making, but they have something which seems lacking in the leadership of large corporations, which is accountability. I don't see why the prevailing corporate structure is an inherently better way of managing, say, 5000 employees than a WOC would be, especially given advances in technology and a highly educated workforce.
I don't think there is anything that strictly says employees in a WOC need to be paid the same, but I believe the ownership would be equal. And I doubt the top earner would take home 7000 times more than the lowest earner. Profits, presumably, would be shared equally among employees or re-invested in the company. Nobody is saying that WOCs are foolproof, but that's an awfully high standard to have.