ADB uses libusb or WinUSB directly from userspace too yeah. On Windows you still need a .inf driver though because the WinUSB driver isn't getting loaded by default for Android devices because they're lacking the MS OS Descriptor
I don't think anyone uses the "native" usb way on either windows or mac os, when it's so much easier to go through libusb.
I've personally done a custom DFU updater for Mac OS some time ago by using libusb. It worked just fine(tm). I don't want to try and evaluate how long it would have taken to do it with the mac api.
