The thing which Linux has managed to achieve, however, is the fact
that there is a large and diverse base of corporate contributions.
That to me is what makes the Linux model so interesting, and has been
a reason for its long-term sustainability.

Although from a somewhat different perspective, it's also why the Linux kernel syscall interface is so unruly, right?

You've got your...some number in the small dozens of common syscalls, which are already present for the most part in v6 or v7. These are the ones I, at least, think of when I think of the Unix manual, section 2.

And then you've got all the other calls added in by (usually) this database vendor or that storage vendor or the other display adapter vendor to make their stuff work more efficiently.

And obviously there's a tradeoff there. Elegance departs, and you've probably introduced some security risk because these syscalls are not nearly as well-exercised as the common ones, but on the other hand you have these large companies paying to work on the kernel, and you have them supporting their product on Linux systems because the system can be bent into accommodating them more easily, and it will run better there than on OSes where they don't get to introduce features that benefit their products, which further drives adoption.