You greatly overestimate how much personal the electrical grid has. Take out two guys in the wrong spot, and the whole thing collapses.
That was your own point, before, about mechanization bringing fragility.
Discussion
Personell, excuse my German.
Admittedly my 50% is guesswork, but there's more redundancy than that. The point at which we go from "voltage fluctuations within spec" to "lost sync, you're all islanded now" is quite uncertain.
My home inverter keeps me updated on the grid voltage outside. Its a bit concerning to see it rise or fall 10% in a matter of minutes, but the lights stay on...