Let me preface this by saying, Jeff owes Red Hat nothing and he's free to stop "supporting" RHEL for any or no reason at all.
That said, "grab a copy of Linux" seriously, gloriously, hilariously handwaves away so many things that Red Hat does to create a RHEL release.
Red Hat pulls together hundreds or thousands of upstreams to create RHEL, participates in many of them, tests all that together, helps partners certify software against it, etc. etc. etc.
It's true, Red Hat doesn't "own" the Linux kernel, but it's done a ton to help develop it over the years. But RHEL is not merely the kernel nor any single upstream. RHEL is a product that comprises thousands of packages all tested together and then released as a supported product.
What Red Hat is trying to guard is not the source code to any single or even groups of projects. It's trying to preserve and capture the value it created from all those parts. Coincidentally, that value is what businesses, competitors, and the community are clamoring for and not the source code alone.
They want that single point-in-time snapshot that everybody agrees on as a de facto standard because the overall community has never been able to agree on another workable standard that would allow targeting applications across the board. And that standard has a name, and it's RHEL. And it belongs to Red Hat.
You can have all the pieces and assemble them yourselves if you like. But nobody is entitled to certify it as (officially or unofficially) RHEL except Red Hat.
If that angers you, I heartily encourage folks to build Debian up as the standard we all certify against. Or start your own business that overtakes Red Hat and earns the place RHEL has today.
Mark Shuttleworth took potshots at Red Hat's business model with RHEL for years, and it seems to me that they're doing a very similar thing now with Ubuntu Pro by holding back updates to packages after 5 years and charging for updates to the Universe and Main repos.