And then immediately talked about host slave issues which are not physical but logical and processing. Perhaps you don't understand what physical means?
Truthfully there is nothing to be gained for me continuing this exchange because I in fact have plugged a Keith McMillen k-board into an op-z and a circuit rhythm and noticed it working perfectly, so your truisms are just that you don't know any synths that are battery powered usb hosts, a problem which is entirely unrelated to your inability to understand the difference between physical connectors and the logical models and data processing issues you described as physical in some weird need to repeat what I said while insisting I am wrong.
The data transmitted over MIDI and USB MIDI is the same, it's not the problem. It's the same protocol.
The problem is that MIDI OUT on a MIDI controller supplies power, and USB midi out on a device DOES NOT, because it's a slave device.
This a physical layer problem no matter how you slice it.
Now go and read the question I asked again.