That's not at all a logical/technical argument - it's just further lazy speculation to claim that only reason designers don't take these obvious actions to improve their product is because "x86 ISA sucks". As pointed out it is hard enough to get obvious things done when there is one company and 3 org units involved - let alone a CPU vendor, an OEM, a BIOS vendor and SoC with 10 other chips by different OEMs. Oh and after that the OS vendor.
None of those are ISA (https://en.wikipedia.org/wiki/Instruction_set_architecture) issues - they are firmware/os/SoC issues. The other issue is manufacturing process - AMD is getting to 5nm only recently and the results in lower power consumption are already telling.
IOW ARM doesn't have some magical ISA level stuff to do more stuff with less power or avoid doing stuff entirely that x86 couldn't replicate.
