This unfortunate accident has nothing to do with the Avoid Curve. One can minimise time in the avoid curve by having a longer line. This of course does nothing for the person at the bottom of the wire.
Using twin engined aircraft is not necessarily the solution. For one thing, it doubles the chance of an engine failure. Unless one has an aircraft which can operate effectively at a mass which will tolerate an engine failure which will not cause any drop down due to Nr loss while the remaining operative engine spools up then there there is still a significant risk to the "dope on the rope".
Sometimes aerial work is safer using a helicopter with a simple and reliable single engine.