Mechanically, I don't see how a leveling kit would affect the strut. It's a spacer that goes under or on top of the strut, but the strut itself isn't altered in any way. It's not stretched nor compressed. It's the same as you stepping up on a cinder block or holding one on top of your head- you're taller over all, but your actual height hasn't changed.
With the MRC strut, what I suspect may be happening is the suspension computer may be altering the valving or firmness of the strut since it sees the control arms at a different angle. Maybe it's constantly doing this and that drastically shortens the life of the strut. I'd think that a simple recalibration after the lift is installed to "zero out" the new ride height position would solve this. Or, if you wanna be barbaric, get longer links for the ride height sensors so that they are back at the position they were in before the lift. I did this when I lowered mine- just accurately marked the sensors where they were as it sat before messing with the suspension. After lowering it, I made some shorter link rods that realigned the marks I made on the sensors.