By your logic, if you gave me four quarters for my dollar bill, you'd then complain that I made out with the "full value" of your quarters, and treat it like I stole your coins, instead of the mutually-agreed-upon trade that actually occurred.

Even if you gave me five quarters and I gave you one dollar bill, an uneven trade in my favor, I didn't end up with the "full value" ($1.25) of your money. I ended up plus only 25 cents.

Learn what "full" means.

A business started by 2 or more people who agree to equally split everything. So for example, if you hire someone new, everyone's share of ownership/profits/etc. is divided up such that the new person now gets paid/equity the same as everyone else.

There are no specific barriers to entry for that, no more than there are for starting a business any other way.

But there is a reason that despite all the rhetoric about evil employers stealing labor, this arrangement is quite uncommon, and tends to scale up very poorly. Here is an article with some pros and cons: https://smallbusiness.chron.com/advantages-disadvantages-business-cooperatives-24608.html

Okay, so then why am I not simply creating that widget myself and selling it for $1000 on my own, if it's that simple? Likely because of both of the following, to name a few:

1. I don't have access to the raw materials and tools needed to create it, they were provided by my employer
2. I haven't spent the money on the marketing that would make customers willing to pay me $1000 for that widget (see: Apple infamously, and largely successfully, charging significantly more for products than comparable equivalent products of other brands)

The bottom line is, there is much more than "your work" that goes into that widget ultimately being successfully sold for $1000, and that's why you can't accomplish the same on your own (or else you would, right?), and it's why you do not have a rightful claim to that $920.

Now, if you're able to create and sell that widget for any more than the same $80 of time/resources, then you should go into business for yourself, and can reasonably say that the business offering you only $80 was ripping you off.

But in the real world, that's rarely the case for very long. Those situations are extremely rare, and when they're discovered by individuals, they're capitalized on (pardoned the pun) pretty much instantly--all it takes is one person to 'close the gap', generally speaking.