All the Pi's have the same USB IP, so I can't imagine there being any significant improvements between hardware versions. I believe only Pi3 can boot from USB, but the bootrom's USB drivers are not very compatible, especially with devices that are slow to enumerate. I do notice that the linux drivers have improved over the years and I am running with fewer problems from USB. The other big factor is sometimes people draw too much current from USB and instead of shutting down the device becomes unreliable, especially from USB harddrives. A bigger powre supply helps tremendously. And the new firmware updates now throw a little square in the corner of the screen when you are starting to get voltage sags.