Correct, but using it, or not, the cable heats up. It’s only when using it that the cable is put under additional strains and stresses. Often times people rest the cable on their palm, bending it at odd angles, not intentionally but absentmindedly. These are stresses on the cable that wouldn’t exist if it were simply sitting and charging. The usage doesn’t draw more power, it just increases the likelihood of miss handling the cable. Now, if a cable is built out of materials that are less biodegradable, or contains certain chemicals that are bad for the environment, they are less likely to break down under similar circumstances. It’s kind of a catch 22. You can make cables that do not contain harmful chemicals, but breakdown easily, or you can make cables that don’t break down easily, but potentially contain harmful chemicals. The real issue is, no matter what, e-waste is being created with disposable cables.

I don’t use my phone while plugged in (mostly because my battery life and usage habits don’t require it), and actually don’t typically plug in at all because I charge wirelessly overnight. But I do have an every pack-in lightning cable I’ve received with an iPhone since they started using lightning, and none of them are broken.