Hi @steependdown, I am not sure I understand all of your questions but I will do my best. By “influence of the leading foot” do you mean what I would call the dominant leg? It seems like this is what you mean, but that said, leg dominance is not as simple as people think. As an example, I am right handed but ski and snowboard “goofy foot” [R foot forward, which is backwards for “righties”.
Instead of thinking about it as one foot being dominant, I am now thinking about how all athletes have a tendency to spiral their entire bodies over time. This can mean that in any given movement or posture, or activity, the athlete will be asymmetrical. This asymmetry has implications in movement effectiveness, efficiency, muscle recruitment, nervous system function, breathing function, and other aspects of physiology [and even psychology].
All cyclists are twisted around the axis of the seat tube; it’s just that some have pain or dysfunction associated with this twist, and some don’t. Also in some athletes it is more visible than in others. Also note, there is no correlation between presentation of twist and pathology.
If you are really twisted on the bike, friction at the saddle can appear on either side. Some riders hang their anterior side [your R based on what you wrote] off the saddle, which means more friction on the L inner thigh typically. But other R dominant athletes will experience more friction on the R from the increased motion of that side of the innominate.
Shorter cranks can definitely help but won’t address the mother of the problem.
When I descend on a MTB, I also sit “goofy foot” and tend to put my L foot forward. I intentionally change this from time to time and swap to the R foot, to challenge my balance and stability. I am of the belief that becoming too engrained in R or L dominance leads to dysfunction and challenge over time, and thus work to avoid it.
Also, for the record, descending with horizontal cranks on MTB is the ideal solution in most cases, rock clearance being one of the factors. Also, having suspension means you can descend like this effectively. On a road bike, it is far more effective to push on the outside foot and inside bar, with the outside foot being at the bottom of the stroke. This is a superior method of cornering over fast or very fast descents on a smooth surface IMO. The best lever point to manage the higher centrifugal force experienced on road bikes [I am referring to the force on the rider + bike, not on the wheels].