Not only do they all rely on Torvalds and everyone else for the kernel (heavily funded by donations, companies, etc), but most Linux distributions are just cosmetic variations of the largest upstream distros.
If Debian died tomorrow, Ubuntu is on life support.
Plenty are not. I am impressed by how usable community-based (non-corporate) distros are (e.g. Gentoo, Arch). This is truly indigenous technology.
> they all rely on Torvalds and everyone else for the kernel (heavily funded by donations, companies, etc)
This is an interesting thought. I believe the Linux kernel would continue to be viable on a purely volunteer basis, without corporate subsidies; I can't prove it though.
And you're right about "most" being wrong. "Many" would have been a better word, particularly if talking about the most popular.
(Another non-upstream-reliant distro that I find fascinating is GoboLinux. Very against the grain/orthodoxy!)
If anything the major distributions are defined by their package managers, of which there is a large and healthy number - aptitude, dnf, pacman, protage, and a heap of weird and wonderful other ones with minuscule usage.