Linux is a pretty standard Unix kernel clone that got traction as an x86 kernel, combined with the GNU userland and various distributions.
Git was intentionally designed to be "simple and stupid." It's extremely fast and reliable because of this simplicity, and because Linus knows how filesystems and kernel caches work.
So I agree that Linus has helped bring about some remarkable things. But it's not because he's an ultra-productive genius. He has a knack for C coding, an impatient and "lazy" attitude, and a lot of help.
And I think he belongs to this kinda older school of hacking, part of which is his rudeness toward bad patches.
The GPL is also a big part of these success stories.
Domain knowledge, or the genius to reinvent it from scratch (CAS and merkle trees for Git)
"heroic" is ill-defined, so don't know about that, but the effort was arguably extreme, in the sense that Linux and git are among the best at what they do. Lots of other people who might have the same experience and abilities did not achieve things like that. I just don't see why you would want to minimize the achievement in any way.
I would add an additional reason that may be unpopular here: It is written in C. A version control system doesn't need to be in C, and indeed Mercurial is written in Python, but C makes it faster.
To bad there are a whole lot of stuff being "introduced" to Linux space that is trying for the exact opposite, being "complex and smart"...
I'm somewhat disappointed that mercurial didn't become the de facto versioning standard instead.
But hg-git doesn't talk to the git CLI at all --- there's a Python library which speaks the wire protocol. So it'd be entirely possible to build a git workalike with a traditional DVCS user interface which seamlessly interoperates with git repositories. I wonder if anyone's already done this?
...dammit, I have too many stupid projects on the go as it is.
[0] https://github.com/torvalds/subsurface [1] https://www.youtube.com/watch?v=ExWfh6sGyso