1) The "natural" movement of a
shackle is an arc. Not the spring. The only reason the free end of a leaf spring moves in an arc is because it's fixed to the shackle(which moves in an arc)
2) It doesn't surprise me that the sliders have a harsher ride. You're essentially replacing the rubber/poly bushings with a hard metal to metal bearing. Remove any rubber suspension bushing and replace it with a harder material, and you're going to get a harsher ride.
3) I'm guessing the most probable reason a slider dies under hard use is due to twisting forces, not necessarily pounding forces.( the pounding forces don't help though,...) When you compress one spring and droop the other, both springs try to twist in their mounts. With the stock setup, there's a big rubber bushing up front and 2 smaller bushings in the rear to absorb that movement.
Remove the shackle and install a slider, and you have effectively fixed the rear spring eye(rotationally, not back and forth) The spring has to twist instead of compressing the bushings. 'Lot of force to absorb there.
Maybe if you installed something like this:
"Orbit-eyes" from
Alcan spring
In the rear spring eye position, then attached that to the slider(or build a custom slider around it), it would account for the twisting force. Other then that, the sliders I've seen for drag use have pretty small bearing rollers, and would be woefully under-sized for desert racing.
Assuming all that would work, there's still:
A large complicated roller assembly with moving parts, custom sized spring eyes, probably 5-10 lb/side,... that has a probable failure mode(roller failure) that includes the rear of the spring flapping loose.
All this to replace a 1lb assembly who's most common failure(bushing failure) still leaves the suspension intact and working.
A slider can probably be made that would work for desert racing, but it's replacing a simple swing arm. "KISS"