The high data rate cables all need to be stiffer. You can find good 100w or 240w charging cables with good flexibility, so that's a good reason to keep usb-2 data-speed but high-power charging cables.

The measure of a good high-power cable is the resistance. You can gauge it with a usb test load, typical usb power meter, and a usb-pd trigger (all can be pretty cheap, often you can find the trigger functionality combined with one of the other two). Calculate voltage drop for a given current by measuring both sides of the cable, or at least compare different cables with similar load.

But I found a "USB Cable Checker 2" by BitTradeOne which will directly measure and show the resistance in milli-ohms, very convenient! A very good cable measures 150 to 250 mOhm, the worse ones are 3 or 4 times that (at which point this device over-ranges around 1000 mOhm). You can really tell the difference with how some phones and laptops will slow their current draw after voltage droops.