What part of USB differs from midi? Signal is sent at a low voltage, but the power delivery is at the same level - 3.3v to 5v maximum. You say itās made to also deliver power but itās like saying a pie is made to be eaten but a carrot is not. There is nothing superior about the internal parts of a USB cable, believe me, Iāve cut open and spliced enough of them to know that for a fact.
There was no implication that a midi thru, proper or improper, would create latency. Your hypothesis was that since the power is only there for the optocouplers, then it is no good for anything else, therefore the signal may become compromised and if it is unable to deliver consistent power or sufficient power the signal degradation will potentially cause an issue. The issue, if not complete failure of the signal chain, will be a resulting latency. You say I donāt understand, but Iām only following your logic on this.
So whether or not midi latency is expected out of a functional thru device is not something which is being questioned or expected, my statement was that in a case where something is failing but has not prevented the device from working in full, the result will manifest in either missing /misaligned data delivery or in something more benign such as a latency in the signal.
There is nothing in this world which is guaranteed to work 100% of the time all the time, but thereās nothing to say that a device which is powered by usb is any more reliable than a device which is powered by 5 pin din. I still have keyboards from my computers in the 1990ās which have 5 pin din that passed power from the PC to the keyboard, itās not just midi, itās 5 pin din which youāre contesting. Thereās no reason for 5 pin din to have any less reliable voltage than the source at which the voltage originates from. Certainly no less reliable than power which is passed over usb - they use the same grounded shield and grounded pin with power and signal passed on other pins, the form factor is simply square vs round.
USB is no more made for power delivery than 5 pin din. This is something youāve been sold by the industry that is selling you USB as the standard.