Having a language that's simple, has a low runtime-overhead and can be implemented in a simple compiler is a quality that quite obviously is still valuable. C would have vanished like a lot of other languages that got out of fashion.
I don't think UNIX has much to do with it, otherwise C wouldn't have survived the 80's and 90's when other operating systems (Windows!) ruled supreme and UNIX operating systems were the underdog.
That place always belonged to mainframes and later UNIX, due to its "cheap" price versus mainframes.
Your story seems to be that C won because of UNIX, which won because of the server room. But the server room was a small chunk of landscape, and code was being written for the whole landscape, not just for the server room. And C won all over the place - the server room, the desktop, and the embedded space. It didn't win on the desktop because of influence from the server room.
https://www.embarcadero.com/products/delphi
It's just as capable as any other language. I don't know what your definition of "low level" is, but I suppose you mean inline assembly, manual memory management, and pointers.
Pascal has inline assembly: http://docwiki.embarcadero.com/RADStudio/Rio/en/Inline_Assem...
Pascal has manual memory management: http://docwiki.embarcadero.com/RADStudio/Rio/en/Memory_Manag...
Pascal has pointers: http://docwiki.embarcadero.com/RADStudio/Rio/en/Pointers_and...
The practical Pascal variants like Turbo Pascal and Quick Pascal, which compiled to native code, are essentially on par with C regarding the features. That includes access to absolute memory addresses, port I/O and the speed of the resulting code. I've done over a decade of Turbo Pascal coding, and going on three decades of C, and I agree they feel like essentially much the same thing.