The protocol it uses on top of PCIe, NVME is still being updated (see https://nvmexpress.org/developers/nvme-specification/
) and has enough places where vendors interpret things differently.
Apart from that, the firmware also handles how the data gets to and from the flash chips, which is where the optimizations live. If you make the firmware lie about the data being transferred out of the fast buffer, safely into flash, it will benchmark really, really fast. Just don't lose power or remove the drive
The 'controller' on flash storage is a full fledged computer, including the need for a non-trivial amount of software to do its job.