I am definitely not an expert, so this is part comment, part question, and I am certain I don't know the answer.
Leather starts with a complex biological substance- the hide. It is then subjected to a series of processes to preserve it. These are relatively consistent, but definitely vary depending on the tannery, the properties of the hide, and the intended use of the leather. Waxes and oils are then returned to the leather using a wide variety fat liquors, under varying conditions, for varying times. For modern leather making techniques, at least the tanner is likely to know the chemical composition of the treatments used. For more traditional leather making, like shell cordovan, it is not clear that the tanners analyze the compounds they use, so even they may not know exactly what is in the mixtures they use. Not that they would tell you if they did.
For after market treating leather, one would expect that the ideal substance to treat the leather might be designed to return to it whatever oils and waxes may have left the item over time. But this would depend not only on how it was made, but how it was treated once put into service.
Of course, it is also possible that the ideal restorative might not be the same material that was in the leather originally. Then the ideal substance would depend on all of the above, plus how the leather is to be used.
The consumer has nearly no chance of knowing any of this. Even the "how it was treated" part really means "what substances left the leather due to its treatment". Knowing this would require chemical extraction of the new and the use leather to figure out what had changed.
Given this, it seems unlikely that there possibly could be one compound that ideally restored leather, no matter what hide, how tanned, how fat liquored and how used.
People have used leather for thousands of years because it is very robust under the stresses to which we subject it. If it were that critical what to use once it is made, then we would have found something else.
I can imagine that a company that made conditioners and polishes, or a tanner, might have the resources and inclination to do this research. However, once knowing what was LIKELY to have left a particular batch of leather over time, this would not tell even the conditioner maker or tanner know how to treat a piece of leather with nothing known about it.
I would think the best one could hope for is not doing harm and preserving water resistance, to the extent it was water resistant to begin with. More ambitiously hoping to prolong leather life and the right amount of flexibility might be asking a lot for any single compound.
Just my non-expert thoughts.