It's not that simple: just because you add a safety margin on a construction element, doesn't mean you're allowed to use this safety margin.
For example if a chain has a certified Weight Limit Load of 1 T, it means it actually lifted 4 T (or 10 T if it's certified to lift people). This is because a lifting sling is tested in very controllable environment when it's new, whereas on a building site it will be subject to dynamical stress caused by winds, it will be hit, it will be used in various temperatures etc.
Now, I'm not saying you're wrong: in case of power cables there might not be such a rigidly defined safety margin in law, and experts may figure out some assumptions, like the drones not operating during wind storms, in which the safety margin is more than needed - and therefore there's some spare capacity BEFORE the the actually needed safety margin.
For example if a chain has a certified Weight Limit Load of 1 T, it means it actually lifted 4 T (or 10 T if it's certified to lift people). This is because a lifting sling is tested in very controllable environment when it's new, whereas on a building site it will be subject to dynamical stress caused by winds, it will be hit, it will be used in various temperatures etc.
Now, I'm not saying you're wrong: in case of power cables there might not be such a rigidly defined safety margin in law, and experts may figure out some assumptions, like the drones not operating during wind storms, in which the safety margin is more than needed - and therefore there's some spare capacity BEFORE the the actually needed safety margin.