> benefit of OSS being that you have access
> to the source to fix/add things
The place where this is the most beneficial is when considering businesses looking to invest in a technology. If you invest in a company/software product that goes under, then you could be saddled with a piece of tech that you can't fix bugs for, etc. If it's open source you at least have the chance to do so, even if the community around it collapses and there is no new development.
The idea that access to the source is some sort of cure-all is a fallacy, but it may also just be a straw man. I don't know that anyone says that all open source projects are going to be manageable just because the source is available, but they are by definition more manageable than a project with no source available.