Note that the conclusion of the toy model rests not on “we did the 9-dimensional integral and got a very low number” but “we did Monte Carlo sampling and ended up with 21%“—it seems possible that this might not have been doable 30 years ago, but perhaps it was 20 years ago. (Not Monte Carlo sampling at all—that’s as old as Fermi—but being able to do this sort of numerical integration sufficiently cheaply.)
I’m quite sure doing this is really cheap even with hardware available 30 years ago. Taking a single sample just requires sampling 6 uniform values and 1 normal value, adding these, and checking whether this is less than a constant. Even with 1988 hardware, it should be possible to do this >100 times per second on a standard personal computer. And you only need tens of thousands of samples to get a probability estimate that is almost certainly accurate to within 1%.
I’m quite sure doing this is really cheap even with hardware available 30 years ago. Taking a single sample just requires sampling 6 uniform values and 1 normal value, adding these, and checking whether this is less than a constant. Even with 1988 hardware, it should be possible to do this >100 times per second on a standard personal computer. And you only need tens of thousands of samples to get a probability estimate that is almost certainly accurate to within 1%.