USB-PD permits 100 W with 20 V at 5 A. If that's carried over just two round copper wires (I don't know whether it is in USB-C) they would need to be 18-gauge or thicker for safety—about 0.94 millimeters. If they're copper, that's about 7.3 grams of copper per meter, 14.6 grams including the return path. Copper is expensive: almost US$7/kg. So a 3-meter 5-amp DC or two-phase cable would weigh 45 grams and contain 15¢ worth of copper. You could drop both the cost and the weight by going to aluminum. If you were designing the system from scratch, you could use 3-phase AC to cut the weight by half again, and use 48 volts to cut the weight by another 58%.
I don't have any idea how thick the 19 wires have to be for USB 40Gbps (GBps?) but I imagine the answer is "not nearly that thick".
Bottom of the barrel vendors will absolutely give a fuck and will cheap out without telling you.
The advantage of USB 2 is that it's so simple that it's very hard to screw it up. You pretty much have to intentionally do it if you want to create a dangerous cable. Even the shittiest cable will work with the vast majority of devices (it might slightly heat up, voltage may sag at the receiving end meaning it will charge slower, but it'll somewhat work).
USB-C is significantly more complex and requires active electronics in the cable itself in some cases, and the potential for higher voltages means a faulty/recklessly-designed cable could request higher voltage from the charger and blow up whatever's connected at the other end.
It sounds like you could maybe make substantial progress by just separating the differential pairs (?) by a millimeter or two of dielectric, giving you a ribbon cable, with much lower crosstalk than the round kind. Bonus points if you color the dielectric rainbow colors.
I feel like it's harder than shielding and tolerances, given that longer passive cables don't seem to exist despite the very high prices people are paying for active cables.
There might be issues of attenuation; we're talking about signals in the GHz range, where you have to use waveguides instead of wires to get low losses.
I don't have any idea how thick the 19 wires have to be for USB 40Gbps (GBps?) but I imagine the answer is "not nearly that thick".