If a subsystem C developer makes a change and introduces a bug in another driver or subsystem (also written in C) as a result, then you would expect them to be able to help at least insofar as explaining what they changed.
I've been in a spot kinda like this. I've maintained C++ with python interfaces. In my case I wrote both. I know how interlocked the changes were. If I touched code that was exposed to the python, I updated the python interface and the consumers of that python interface.
It was nothing like making changes that cut across into another developer's C++ code (hell, I would even update their python interfaces/consumers too). That was temporary coordination. The python part was much more frequent and required much more detailed understanding of the internal APIs, not just the surface.
Having someone else responsible for the python part would have come at a huge cost to velocity as the vast majority of my changes would be blocked on their portion. It's ridiculous to imply it's equivalent to coordinating changes with another subsystem.
That isn't "effective co-maintainership".