Isn't the point that x86 instructions are themselves no longer a good mental model for what the processor is actually doing under the hood, and thus C which was long billed as a thin layer over top of assembly is itself a higher abstraction?

There is AFAIK no way to express or interact with speculative execution/branch prediction, for example.

Sure, but then you're really arguing that the ISA no longer maintains 1:1 instruction-level implementation and that this is the definitive quality of whether or not something is low level, to the point that any deviation from that model makes it not officially "low level". To me that's just a very tedious pedantic argument that simply fails to capture the actual meaning behind why/when we might call something low level.

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.