No, it's not been debunked. Lennart has just made it clear time and time again that he has his own definition of "monolithic" and so the rest of us should just shut up.
Coreutils has a lot of binaries that do different things. Is is monolithic? The GNU ecosystem and autotools barely function without other GNU tools which aren't part of the same project. Are those monolithic? Monolithic is a canard.
You're the one with the different definition IMO.
The BSDs do have somewhat monolithic repositories, along with somewhat monolithic development and release processes. All the Linux distributions have, ultimately, monolithic release processes.
However, components within these ecosystems are much more loosely coupled. Mixing different implementations (or different versions of the same implementations) is not only practical but sometimes essential to getting useful work done.
I have a nuanced definition of monolithic that recognizes various ways in which something may or may not be monolithic.
Lennart and his cohorts have a very absolutist but conveniently-shifting definition of monolithic that they demand everyone blindly adhere to lest they be accused of spreading FUD.
A "monolithic" system is a system that cannot be factored into stand-alone components. That is, there is a high degree of logical coupling between its components that make them difficult or impossible to use independently.
A "modular" system is a system built of multiple logically-distinct components. Note that this descriptor says nothing about their degree of coupling.
Examples:
* Linux, the X.org server, and systemd are both modular and monolithic.
* Coreutils is modular but not monolithic.
* The "ls" program is monolithic and not modular.
Note that under these definitions, "modular" is necessary but not sufficient for "not monolithic". From the way he talks about it, however, Lennart seems to believe that "modular" means "not monolithic".