I think it’s reasonable.

First of all they didn’t want to put a battery on the headset. Fair enough, even without a battery it’s heavier than most headsets.

That decision means the cable doesn’t just need to provide average power consumption, it also needs to be able to handle peak power consumption. It seems reasonable that the headset has similar peak power to a Mac Mini - which has a 185 Watt power supply.

USB can provide up to 240 Watts, however it needs relatively high voltage to do that over thin cables permitted in the USB specification. 48 Volts for 240 Watt power delivery and 20 Volts for 100 Watts.

Vision Pro is only 13 Volts - which means that cable almost certainly has thicker wires than a standard USB cable. If you tried to power a Vision Pro over a standards compliant thin USB wires it would likely be a fire risk at only 13 Volts.

Apple could solve that by using 48 Volts… but then they’d have to convert 48V down to 13V… and they need to do it with very light weight and small components. Those conversions are not free, especially with DC power. It might even be that the conversion is so inefficient that you need more than 240 Watts to power the headset.

But even if 240 W is enough (it probably is), it would also reduce battery life. And battery life is already an area where the headset isn’t really good enough. So, in summary, yeah I do think it’s reasonable to use a proprietary power cable. This headset is just too close to the technical capabilities of a USB cable.

Worse… a lot of USB cables aren’t even compliant with the specification. You could burn someone’s house down if the cable is non-compliant.