An amateur trying to drill out such a large plug will guarantee ruining the tank. Few would have the skill or patience to do it properly. But a good mechanic with a double-cut carbide burr on an a high-speed air tool could finesse the last of the plug out after drilling the center out.
And when I said to use an acetylene torch, I said to heat the plug, not the tank.
But you are right, most people would probably melt the tank by getting the plug too hot. I have used one all my life, and can work miracles with it. But I am not 'most' people.
It is too bad people don't maintain their stuff properly.