I'd say it's partially a design problem with the angled mounts. As Norm says the torque twist is what does it. With horizontal mounts they only compress/de-compress in one plane of motion: upwards/downwards. With slanted mounts on Sweptlines there are two planes of motion: upward/downward, plus the twist along axis of crank. I think that's where the rip/tear actually starts.

When I ripped mine out is was a situation very similar to the Hollister mudpit, that full power was applied in a lower gear plus I had a very heavily loaded trailer on behind. It was an offroad excursion [not by choice] on a very nasty stretch of rutted dirt road and something just had to give: motor mounts.

I later added just such a torque limiter chain to my last V8 in the Townie as you describe, John, never had another problem. You can also use a rod threaded at each end with eye nuts and bolt it direct & solid, which I also did, but that's too extreme for a daily driver. Now with the Cummins the mounts are entirely different, as horizontal, so no further problems there either.