what a fun discussion!
i actually think RE raises a perfectly legitimate question in his original post.
where it goes wrong is to then infer that leather-soled shoes will consistently be beaten by sneakers or rubber-soled shoes for comfort, or that a even a basic understanding of physics points to the inescapable conclusion that leather-soled shoes must necessarily be more uncomfortable than the "comfort" shoe alternative. i just don't believe that's true. my own experience and observations have been the following:
1 - a leather-soled shoe that really fits and is well constructed is the most comfortable shoe of all.
2 - a leather-soled shoe that fits poorly and is poorly constructed is the most UNcomfortable shoe of all.
3 - a sneaker / rubber- / cushiony-soled shoe will typically be comfortable, but it will never be quite as comfortable as the best leather-soled shoe, nor will it ever be truly uncomfortable. in statistical terms, the range of experiences for a sneaker-like shoe has a tighter distribution.
this of course begs the question as to what conditions need to be in place to achieve 1). again, my experiences:
- the shape of the last (an issue that is largely irrelevant for sneaker-like shoes). a last that doesn't fit your foot will force your foot to distort into unnatural shapes, preventing the foot from being in equilibrium and introducing unnatural stresses. for example, an overly-pointed italian-style shoe for a wide foot will force the foot to curve in a concave form (with respect to the ground), resulting in excess stress on the balls of your feet
- the thickness of the sole: a thin leather sole can be murder because there will be no shock absorption. a thick sole, on the other hand, will be extremely comfortable.
- the shape of the arch, or instep. for me, personally, i like / need a high instep. the shape of the arch is critical for good support.
- believe it or not, the material of the heel can also make a big difference, including and especially to the shock absorption
in other words, there are many more things that can "go wrong" with a leather-soled dress shoe.
i also have an instinctive hypothesis that while rubber is good at cushioning the impact, it does not do a good job of distributing the impact. when i wear a rubber-soled shoe and step on a stone, i feel the impact / object very directly where the object is. with well-constructed leather, the impact is distributed to a greater degree across the entire surface area of the sole. i believe this is why so many find leather-soled shoes so most comfortable. it is certainly an important contributor to my own preference for wearing leather-soled dress shoes -- a choice i would make even if i had a stigma-free option of wearing "comfort" rubber-soled shoes.
leather is an amazing material. there is a reason it has stood the test of time. RE, i think the physics you think are so simple are actually not... and the situation overall is more complex than you may think.