Did you just benchmark you boot drive? it will definitely score lower because the system is using it for other things at the same time.
Ideally you boot to a clean OS on another drive with no applications running at all aside from the benchmark.
Also, what you are benchmarkinig on also can have an impact. laptops often can't handle the heavily load due to the chipset not being as performance oriented as a desktop model.
We also don't know if your M2 port is attached to the chipset or to the cpu in this case.
Still, you will never use 250k iops as a regular user so why stress about it.