ah right. the point still stands, though. i was also under the impression that many of the device drivers that ship with with modern android phones are closed source. see the step in building lineage "Extract proprietary blobs"[0]
Those are the firmware pieces running on the cores that aren't even running Android as their OS for the most part, so it's not really applicable to the root discussion.
[0] https://wiki.lineageos.org/devices/payton/build#extract-prop...