If one wants to get technical, Linux is only the kernel, which is why Richard Stallman pushes people to refer to most of the complete operating systems that use it as GNU/Linux [1]. And Linus Torvalds and Andrew Tanenbaum had a very famous flame war [2] over the issue of monolithic kernels vs. microkernels, in which Linux was the monolith, and there are a lot of parallels between this article and the design considerations at stake. Not all of the advice here applies well to kernels, IMO. But one can certainly say that from a practical standpoint, Linus Torvalds has a few reasons to feel that he and his monolithic kernel won that particular debate.
Linux isn't a monolith. And it isn't a monorepo either since Linux comprises far more than just the kernel.