I'm guessing you're probably familiar with the Metcalf substation attack in San Jose a few years ago
In your opinion how dangerous would that be if carried out simultaneously on maybe 4 or 5 regional major routing substations?
It seems to me at least that it would cause a massive regional cascading failure that would take perhaps weeks to restore.
The individuals who pulled off the Metcalf substation attack demonstrated a significant amount of operational planning and discipline. No reason to think they wouldn't be capable of doing the same thing replicated on a larger scale. (I think there is a chance it was an Iranian sleeper cell beta test)
I meant sophisticated because they knew to cut the fiber optic lines first and a few other details. They had obviously done some planning, it wasn't just a few dudes sitting around bored and drunk. It was planned out.