I don't know what you are trying to say. FOSS guarantees that you'll have access to the source code, with the legal ability to modify and redistribute it at will. That is the basic guarantee.
The difference between FOSS and proprietary is a legal distinction and nothing more. FOSS can be made by big companies (Microsoft even! see: the OT of this thread) and proprietary software can be made people like Joe in his basement (I've been that Joe in his basement before, well besides the basement part).
The whole tangent of "big companies vs Joes" is kind of ridiculous and nonsensical in a way.
You could do similar things to what FOSS provides using reverse engineering with proprietary software. For instance making a modified version of MS Windows and putting it up on BitTorrent or selling it in a store for profit. But you chance getting caught and sued or worse. The Windows EULA does not permit you to redistribute or modify Windows, even for non-commercial purposes.
Not so with FOSS. I could (and actually have) made customized versions of Linux and other FOSS that I have outright redistributed. The license agreement permits this.
Really, that's the difference. Anything else is just random nonsensical posturing.