Thanks by the way for the test. Useful for me.
Here the specs link of the manufacturer of x470:
https://www.amd.com/fr/products/chipsets-am4
Those specs are the capabilities of x470 chipset. so, to persist in knowing if the chipset is pcie 2.0 or pcie 3.0, nothing better to check the information. Certain one supposed that the smoothness of engraving was the cause of the "slowness" of the x470. I have serious doubts that this is the cause of the speed differences.
I think rather that it is the chosen architecture of each of the manufacturers.
the x470 seems to function as a quick switch and it reserves only part of its bandwidth for each of the technologies (USB, SATA, PCIE). Each has its turn of bandwidth.
whereas the z370 seems to grant a direct link through the DMI link. This explains why the Intel motherboard has shares between SATA and M.2.
The z370 operates as a fixed turnout. Whereas the x470 works like a spinning top by scanning each of the I / O and sending them back to the CPU. At the cost of lower bandwidth but no shared line handicap.
which explains the reason why there is at least 1xm.2 connected directly to an AMD microprocessor.
While at Intel, due to the technological choice, it has little importance to put all m2 on the chipset.
These differences have little impact for the user(considering you put your I/O dilligently) but require more consideration when dedicating a machine for virtualization and servers.