> And structures, unions, pseudo-meta programming via the macro processors,

Those exists in macro assemblers, for they are extremely thin abstractions, no thicker than jumping to a label instead of jumping to an absolute or relative address.

> no exposure to IO unless on a CPU with MMIO.

Well, since not all processors have I/O instructions (or dedicated I/O pins), the easiest way to implement portability is simply to not provide a direct access to them in the language, and let library functions handle it.

> Those exists in macro assemblers, for they are extremely thin abstractions, no thicker than jumping to a label instead of jumping to an absolute or relative address.

They’re much more than that because of type aliasing, which is what lets you write -> . = operations all day without each one literally being a memory access in asm.

Which kind of proves the point C doesn't provide all the necessary capabilities for a systems programming language.

As for macro Assemblers, IBM i one supports OOP constructs, so are OOP languages now low level?

Also functions, loops, conditional statements, and arrays are considered abstractions.