I mostly concur. My experience is that, once you add enough water, everything that is basically well formulated performs about the same. For most soaps this is a hydration level between the point where the lather takes on a sheen and the point where the lather starts dripping off the blade on the first stroke.
I will also note that Modern Williams has among its (imo few) virtues outstanding 'residual slickness', despite being probably about zero superfat and having no milks or whatever in the formula and having decently high lauric/myristic acid content, so I don't think the prevailing theories about what causes 'primary' and 'residual' slickness are quite right.
Yah, I also don't believe it's a certain ingredient that allows for better residual slickness.
I find that basically any decent soap hydrated enough gives me an the residual slickness I need.