> Each cable needs one of 3 resistors depending on them being a A/B-to-C cable, 1.5A C-to-C cable, or 3A C-to-C cable.
No, for C-to-C connections, the resistance is provided by the host ("downstream-facing") port, not the cable. The resistor in an A-to-C cable is basically emulating the signal that would otherwise be provided by the host.
There's no such thing as a "1.5A C-to-C cable"; all type-C cables are required to deliver at least 5A. The limiting factor is the host, not the cable, which means the cable must not incorrectly advertise capabilities that the host doesn't support.
> Never mind that a C port has so many extra pins compared to a A or B port, that one would think that id-ing a A-to-C cable would have been as simple as looking for life on any of those extra pins.
That's exactly what the new CC pin is used for. Right now the spec says "legacy cables should connect CC via a 56kΩ resistor", but it wouldn't matter if instead the requirement had been "legacy cables should leave CC disconnected"; the issue is that cable manufacturers are ignoring the spec.