That's fair. C is very old and used for almost all hardware so I think while you can make the argument that "only clang and gcc extensions asm blocks available like that, and intrinsics are only available through vendor-specific headers" and be right, by that same logic literally nothing except binary machine code for hardware without any kind of microcode can be low-level, and even then it's probably always hardware dependent (because if it's not fully bijective to the actual hardware it's implemented on top of, the semantics leak).

Practically speaking, we have a word for the kind of "abstractionless" model you're describing: machine code. I mean, even assembler is a bunch of abstractions about 'registers' and 'instructions' that are really just specific portions of the hardware or opcodes!

So we either descend endlessly into pedantry arguing that cosmic rays and electron tunnelling represent inexcusable deviations from the overly abstracted semantics that hardware vendors expose in their products or maybe we draw the line somewhere else.

You may not agree with mine, that "practical and simple interop with machine-level language impls across a high-level language interface is sufficiently close to the hardware as to be low level" but there has to be a limit somewhere between that and "technically the hardware's operating temperature is part of its logical semantics because if it exceeds a certain value for long enough it starts to degrade and yield incorrect results or terminate execution". I think eventually it just becomes unproductive nerd sniping, personally