I'm using LMDE 7 and I cannot reproduce this.
My setup is a no name USB 3.0 32g usb stick formatted exFAT. I tested using cp to copy a 170k file to the usb stick and it took less than half a second. I ran it with time to make sure. When I ejected the drive it took maybe 1 second more before it was ready to remove.
ETA: I just tested a 1G file and it took 45 seconds to copy and run sync.