It seemed to take an annoying amount of time to get the Windows 10 Media Installation Tool to actually create media. We were getting a funky error (0x800704DD-0x90016) every time we tried to make a DVD or ISO.
It turns out running the tool as Administrator isn’t enough. We got it to work by logging in as Administrator then running the tool. Just to make sure this wasn’t a fluke, we tried it on several machines and sure enough this was a workaround.