Ooh ooh...just the kind of statement that'll get me posting
Noting that I'm about as far from a Kantian as one can get, even from a broader perspective this isn't a case of a single truth that oughta be universally applicable to the topic of "treating automotive leather". Rather there are truths.
There are different types of leather, and plenty of other potential differences too (UV exposure, type and degree of soiling, wear, etc.).
So what works for one person in one situation might not work for somebody else. IMO it's another case of it being tough to generalize too much.
FWIW, *IME* (which might not be relevant to anybody else), most of today's automotive leather doesn't require much, if any, "treatment", it just needs to be kept clean. I've only treated the leather in my '01 S8 *once* and it's like new other than some signs that the front seats do actually get used. OTOH, I've treated the leather in other Audis (I've been told it was the same leather) regularly and the one bolster that gets the most abuse still needed replaced after enough use/time- as best I can tell the treatment didn't really provide any benefit. Completely different situation with my '85 Jag, which *must* be treated regularly....different leather, different...uhm, truth.
Here's one to make us :think:

I *never* treat the leather steering wheel covers in our Audis and I've never had a problem even after many years and many miles of driving. But I sold one nearly new Audi to a friend of mine and the leather on the wheel needed replaced after a few months! I suspect it was a combination of her handcream (or somesuch wildcard) and UV exposure, but still.... :nixweiss
Vinyl/etc.- While older vinyl/etc. seemed to dry out if not treated, that no longer seems to be the case (again, just *IME*). Using something with UV blockers would undoubtedly still be a good idea, but today's automotive vinyl/plastic doesn't seem to dry out the way the older stuff did. I *never* treat the interiors of my dog-haulers (for various reasons) but I keep them clean; no problems even after many years.