2. The charging speed is fundamentally constrained by how thick the cable is. So thick cables are very likely fast-charge cables (they wouldn't spend the extra money on lower-gauge copper if they weren't going to need it for something), and thin cables definitely aren't.
I so far haven't chopped up any usb-c cables, but I don't see why to expect any different.
In a way, this is actually fine too — the conductor itself can be higher-resistance, as long as there's enough shielding to prevent the heat the conductor puts out from setting anything on fire. (Basically, following the same rules for sheath thickness as in-wall cabling uses.)
The only real practical difference, for most people, will be that anything electrically connected to the "thick sheath, thin conductor" cable, will get very hot. (And also, if you use such a cable to connect a device to a portable battery bank, you'll find you get your battery bankk will run dry sooner than expected, since your cable is acting as an additional load.)
The bigger issue is that the insulation material will degrade over time if it's consistently exposed to temperatures that are too high, and at that point it becomes a safety hazard because the conductors are no longer properly protected. So typically cables with a higher temperature rating will have insulation and/or an outer jacket made with different materials.
For mains leads, this usually means you're "grounding" heat into:
1. the device itself, usually at the power supply. The heat dead-ends between the coils of a transformer, this being why high-wattage PSUs have fans.
2. your wall — specifically, your wall junction-box power sockets, at the point that the device's power lead's male connector touches the faceplate of the wall socket. This is why you'll often see slight electrical singing on such sockets when you're operating e.g. a portable air conditioner or microwave on a 120V 16A socket: despite most of the heat following the thermal conductive path of the cable into your house wiring, some of the heat ends up transferring into the air where the thicker insulator ends, through the bare contacts, and into the plastic of the wall-socket faceplate.
3. The rest of the house, through the thermal conductive path of the house wiring — the house wiring, being lower-gauge and so needing relatively thinner insulation, leaks heat more readily than the sort of "super-insulated" cables made for high-amperage appliances, and so the heat is gradually sloughed off all over your walls.
4. Your neighbourhood electrical distribution box. Despite heat leaking through your house, modern residential wiring's electrical insulation is still thick enough, that if you're using enough household load to just be barely below tripping your mains breaker, you're probably heating up your neighbourhood distribution box. Ever noticed one humming really loudly when you walk by? Just like your computer's PSU, these have active cooling that goes harder when houses are dumping heat at them.
Note also that this is among the reasons that industrial power routing (for e.g. factories, mills, etc) doesn't use insulated NM in-wall wiring (Romex), but instead routes individual [lightly-insulated, essentially just for electrical separation] conductors through metal conduit, with as little in-wall routing of that metal conduit as possible. The metal conduit is a heat sink for the conductors — such installations are trying to take on the responsibility of dumping electrical waste heat locally, so that they don't overheat their nearby electrical distribution station, or produce line sag on the poles connecting them to it!
Also there are cables that bulk up on insulation to pretend to be more premium.
Passive ones are available in multiple lengths up to 2 meters, but only go half speed above .5 meters.
It works great, although I'd like a microcontroller added that can display the standard rather than looking up the connections myself.