To most users Linux is just as much of a black box as Windows is.
Even among Linux fans, the number of people who actually need to customize the kernel is tiny. The number of people who can customize the kernel is even smaller.
So where's the freedom? At the OS level, all that's happened is that the lockdown has moved from corporations to a subset of the developer community.
Most end users aren't any more empowered than they used to be.
Now - it's different in the web and language spaces, where there's a steady simmer of framework development, and many popular web projects/products wouldn't have been possible without framework sharing.
But there's still plenty of proprietary content there. Just try to get Google or Facebook to share their data collections with you and see how politically relevant open source 'freedom' is then.
If that seems like a tangent, it's missing the point that the value of a system doesn't come from the source code - it comes from the system as a whole, and includes usability, community reach, innovation, invention, and data.
Open source pretends to be a huge lever for freedom, but it's more like a battered fork caught in an avalanche.
In computing, the world-changing leverage is elsewhere, and always has been.