Genuine leather = just means guaranteed animal derived. That does not mean that the term 'genuine' denotes a lesser quality of full grain.
Full-grain leather = legal term in itself which means top-layer. The words 'natural' or 'genuine' have no bearing on the 'full-grain' legally - possibly the treatment, but not necessarily. It does NOT state 'Top-grain'.
No hierarchy of treatment is legally defined because that is dependent on too many variables. Therefore, I would take issue with the "impacting...longevity"even "potentially". Every nuance of a natural fabric has the potential to affect "character" and/or "longevity". Depends on thickness, sewing techniques, dying and a million other things.
No-one should think they have an inferior product because the word 'genuine' has replaced 'natural'. In fact 'natural' may have been legally challenged so they changed it. It's just unfortunate that
Coach chose to replace one unnecessary word with another (esp. one that is associated with non-full-grain leather.