Yes but not there, later they get 350MB/s with the same setup.

> I put that drive an ICY BOX IB-1817M-C31 enclosure, with a maximum theoretical speed of 1000 MB/s.

Checks out, it has a 10Gb/s USB port.

The mistake is

> the USB controller of the Pi has a bandwidth of 4GB/s shared across all 4 ports

It's actually 4Gb/s = 512MB/s