UNIX was ubiquitous in the data center well before Linus even posted his first version of Linux on USENET.
Everything ran on SunOS, HP-UX, IRIX, AIX, etc.
C was pretty much ignored on 8 bit home computers, outside some toy compilers for CP/M.
In the 16 bit days, it was yet another language alongside BASIC compilers, Pascal, Modula-2, Assembly.
C is so tied to UNIX, that POSIX had to be created so that any non-UNIX operating system could provide a cozy home for their C compilers.
UNIX/POSIX is for all practical purposes the runtime most C applications rely on, there are naturally some exceptions like free-standing or Windows (which eventually gave up and add to start improving its support).
It is only due to historical accident that Microsoft gave up on Xenix, instead of replacing their MS-DOS efforts.
And many projects properly abstract their OS layer so they aren't tied to POSIX.
Maybe Unix is tied to C, but C isn't tied to Unix.
?!? What a claim!
Traditionally this was a profitable niche, Microsoft would like to take a fat piece of that, and instead what happened is that Linux destroyed the profit margin. A million dollars overhead that would have kept a hungry UNIX® vendor alive on your project didn't turn into an extra million dollars on Microsoft's balance sheet, instead it evaporated because Linux is "free". And so then Microsoft lost interest.
WSL is Redmond going OK yeah, here you go, an actual Unix.
The point still stands, that POSIX checkbox was relevant enough for spending the money in engineers salary during Windows NT 3.51 development.
C was invented to rewrite UNIX in a programming language that made it easy to port UNIX between machines.
So what you're saying is contradictory. You're saying the underlying motivation of C was wrong or unnecessary (porting UNIX to different hardware architectures) but C won because that underlying motivation (easy porting between hardware architectures) was partially right.
Your position is now that C didn't need UNIX as a stopgap, which is weird because your argument gains no weight (basically saying C's dominance is sheer coincidence) if it's true but if it's false you're just plain wrong.
On the consoles it took until PlayStation for C to take off among game devs.
Additionally many Amiga games used Blitz BASIC and AMOS.
Anyone involved in the Demoscene early days would be 100% Assembly as well.
On PC, it required until Watcom with its great MS-DOS extender for devs to finally move away from Assembly in mass.
It depends: for the classic 8 bit home computers, games were mostly written in assembly. Later DOS games were commonly either written in Pascal or C, but quite a bit off Assembler code was often used for the more performance-critical code sections.
I was there, Gandalf ;)
(and note how I specifically wrote "dominant high level language", not "dominant language", since assembly coding was indeed very relevant on those machines, for UI apps 100% assembly was quite rare though, and hybrid C/ASM seems to have been more common).
In my part of the Iberian Penisula it was Turbo Pascal on PC and AMOS/Blitz Basic on Amiga.
With lots of inline Assembly anyway.