You bring up an interesting point though, as when wheeling it is very possible for the insert to get rotated somewhat due to flexing etc. This may put undue stress on the bushings, causing this type of failure. Do you think there is any benefit to be gained by loosening the control arm bolts and then re-torquing then after a wheeling trip?
Given that they were torqued on the ground, I think it's just a matter of time until this style of bushing fails if you flex the suspension out often.
I see your point in regards to loosening them after each trip. If the sleeve somehow rotated while flexing and didn't return all the way back to it's static position loosening the bolt after the trip certainly would help to take tension off the bushing. I wouldn't think that should happen with the bolts torqued properly, but in your case it looks like it may have.
Out of curiosity, what did you torque your arms to? I believe I did my uppers to 60 ft/lbs and my lowers to 90 ft/lbs.
Either way I think this is just an inherent problem with this style of bushing where the center sleeve is bonded to the rubber. That would certainly explain why the poly bushings held up better at the other end. Generally from my experience, rubber far outlasts poly. It doesn't look like the rubber wore out in your pics, it just looks like it tore due to twisting.
A rubber bushing where the center sleeves are allowed to spin freely is the best option in my opinion.
