Yeah you are right but you miss one point.You asked ‘what is OpenCore legacy NVME’
There are likely other parameters within EFI that control this. I do not have any info on these as I am not a firmware engineer..
The official Apple drives made when these machines were new (SSPOLARIS) were likely made before any of this APST or anything else came into mainstream..
Given manufacturers often change drive specs without warnings I suspect a custom model reliant one a consistent component source is likely to be best in terms of consistent performance..
Natively this Mac mount an ahci driver not nvme, so I think that nvme driver were developed indipendent from the pcie blade install on MacBook ‘15.
At this point I don’t understand why if you have devoloped a nvme driver and you lost time and energy to do it, it not work correctly. For me this is a bug in the nvme driver project by apple. Not a intentional thing, and this is so weird because the implementation of nvme is open source. They could make a simil copy paste of the drivers that Linux use.
This is a simplification, sure, but maybe there is something that I miss