10 companies are responsible for 57% of the changes to Linux. This is better than the typical 1 company responsible for the majority of changes in a browser, but it's not remotely close to "hundreds and hundreds of independently working engineers". Volunteers only make up ~8% of the changes.
What we don't have is any browser that's a multi-company project, though. WebKit used to almost be that, but then the blink fork happened. The closest currently would I suppose be Chromium as it's also backed by Opera.
I think we're in agreement that Linux is in a better state than the browser. To nit-pick at your argument, Linux development is driven by people who are interested in working on it; many of those are lucky enough to have employers who encourage them to use a company email address to submit changes, and part of their working hours. Nothing indicates they wouldn't still be contributing without the @intel.com attached to their name.
Furthermore in the study you are referencing, the "8% volunteers" is larger than any company's contribution besides Intel and RedHat - even more if you add in the individual "consultants".
https://www.linuxfoundation.org/blog/the-top-10-developers-a...
But there is no such entity as GNU/Linux. It's hundreds and hundreds of independently working engineers who would all have to be hit by buses at the same time.