Even if this weren't a fallacious argument, he's actually in the process of replacing Thekla's C/C++ workflow with a custom language called Jai.

Isn't Jai piggybacking on C?

He started with two backends. One generates bytecode for an internal interpreter, and this is still needed because all Jai code can be run at compile time. The other backend generates C code, but it's a temporary measure. He just added the LLVM backend: https://www.youtube.com/watch?v=HLk4eiGUic8

oh thanks, I didn't see the last one :)