[grey-area]

so all the above that you lay out was already calc'd in their overhead...

The cost per employee is not just salary, no matter how many employees you add. Taxes, healthcare, pension, equipment all scale linearly with employee count.

Of course the company then wants to make a profit on top, or they'd be better off just shutting down. Companies extract extra value from their employees, in exchange for taking on risk and providing funding and stability. In some cases that's justified, in some cases they're not adding much while extracting most of the value - as an employee that's a judgement call you make - as patio11 says above, you can always choose to start on own, and usually you'll make more money doing so.

You may well have been cheated by your former employer (we can't possibly comment sensibly on that), but there are high overheads associated with each additional employee.