Articulation is a complex system that has a lot of different interdependent factors. And maximizing the RTI score isn't always a recipe for the best overall suspension performance, even in more difficult terrain.
The important considerations not captured by an RTI score are the load distribution and body control. To make an extreme example, you could have a vehicle with a highly progressive spring set (air springs) that has a super progressive effective spring rate. It could have 25 inches of travel at each corner, but the load on each tire drop by 90% after only 2 inches of travel. The result is a vehicle that scores really high on an RTI ramp, but performs just like it has only 2 or 3 inches of travel.
A comparison of IFS and a solid axle really teases this out. I'm borrowing a calc I did for a 4Runner to compare, but this is very similar to the LC250. I just don't have time today to make a more complex model.
With a vehicle that has 72" track width and springs with a constant rate mounted inboard at 48" width (1 foot in from each WMS), and a spring rate of 200lb/in and the axle is bearing the weight of 2500lb. On a level surface each tire is loaded with 1,250lb of weight.
Now let's assume an obstacle where frame remains level and one tire is on top of a 12" rock. So the axle system will be put at a 9.56* angle.
With a solid axle modeled as a continuous beam with two point loads (springs) and supported ends (tires) the force on the tire displaced upward will be 1783lb and the force on the down side will be 717 lbs. The springs will be displaced 4" up on one side and 4" down on the other.
With independent suspension on the same vehicle without a cross suspension link like a sway bar or KDSS the force on the upper tire on the rock and the same effective spring rate of 200lbs/in will be 2450lb and the lower tire will be 50lbs.
Now let's imagine the same situation on both, but the solid axle has limiting straps or shocks or ?? at only 11 inches of max cross articulation. The solid axle will be very stable all the way until it lifts a tire while the IFS will be far more unstable and have worse performance on everything from 0-11 inches of articulation but have some small benefit beyond that. The solid axle setup will easily out perform the IFS on the trail overall at lower speeds.
When you have either a scenario where the two axles have significantly different behavior, the result is usually a split where the front IFS having a lot more resistance to articulation. By leaving the rear sway bar attached, rather than fully flexing as it would, it transfers some force through the chassis to the front suspension that forces the front compression side to compress further (It does basically nothing for the other side). And the result sometimes will be a higher RTI score. But it also means worse load distribution on both the rear axle and in most cases the front axle as well.
With KDSS using hydraulics to transfer some of that force to the front axle, it is using the sway bar against the front coil spring and while they both function to increase the compression of the compressed side and extend further the drooping side, the effect on ground pressure and load distribution is very different. The KDSS version reduces the effective system spring rate on the compressed side and increases on the droop side. So, rather than force even more weight onto the compressing side of the IFS, it transfers that load to the other side. The result is still some worsening of the rear axle load balance, but it is offset by significant improvements in the front axle load distribution. With a sway disconnect, you don't get that benefit.
Within the range of KDSS travel, KDSS should significantly outperform SDM in terms of vehicle load distribution. But it will likely also perform worse in extremes due to limited travel and harshness at higher speeds.
