There is AFAIK no way to express or interact with speculative execution/branch prediction, for example.
TFA famously argues that Spectre/Meltdown et al break that abstraction. But note that they are quite literally exceptions to the rule: the only reason we know/care about them is that the "magic under the hood" that was supposed to make CPUs faster while maintaining that abstraction introduced a bug that caused the implementation details to leak to the end users.
Similarly even vp2intersectd took multiple cycles in its original Intel impl and even in the performant AMD Zen5 impl it still takes >1 cycle with 6 levels of pipelining or somesuch. Ok. If literally not even a chip's ISA is "low level" then the term is effectively meaningless.
The only way you could define a "low level" language capable of exercising that hardware's capabilities fully would be to have some kind of per-cycle, pipeline-aware annotation layer over the actual machine code... which really seems like quite a lot of noise/cruft you'd not typically want to add on top of everything, all in the name of still technically being low-level according to some dubiously pedantic criteria nobody would event want in practice.
The part I find tedious is C programmers who cling to the language by claiming it lets you understand and finely control what the machine is doing, when it clearly does not, because x86 assembly itself is being emulated by the cpu underneath. To me, anyway, that's where I find some credence in the "C is a high-level language" meme.