You don't have to take my word for it. You can search the web for RPi USB or Raspberry PI USB problems, or even do your own tests.
Try running dd if=/usb/storage/some/file of=/dev/null and see just how slow it goes. The fact that the Ethernet interface is connected over USB is also a problem, because it hogs what precious little bandwidth the RPi has. Try running a bandwidth test from the RPi to another computer on your LAN; you probably won't come close to 100mbit/s.
No doubt the RPi is good at a lot of things, but USB performance and network bandwidth are not among those things.
