Interesting strawman, but I'll admit to the low-hanging fruit there.
In what you've quoted, I have not compared XIV to other MMOs, or even other games generally. I compared how we treat the concept of a difficulty curve and in-game situated learning. Anywhere else, its the basis for a good game. Here, it's as often treated as satanic.
"The endgame experience have more going on than midgame" or "cumulative learning" or "gradually increasing complexity/difficulty" are not new or controversial concepts.
Nor is it is new or controversial to want not to create systems of incentives that will split your playerbase in an increasingly irredeemable fashion, let alone towards some sort of poorly understood quasi-class warfare -- "casuals" vs. "hardcore" who nonetheless overlap, individual to individual, across every criteria] -- as we have here.
Consider: How much of the game is actually presented attractively to a given player, be they the mythical Conny Casual, Eddie Elite, or anyone in between? What does the game do to draw in someone who might not be inherently interested in the combat aspects (which are still some 90% of the game's content, no matter how you cut it)? What does it do to actually let highly anxious people step over the hurdle to enter Extreme trials or Savage, if they want that level of depth, but want to be and feel prepared (besides yet again telling the community to make up the difference on their own)?
Initially, there's little. HoN is a boon, but a small one, because it's neither directly situated nor does it do much to actually draw players' interests. You go if you have that interest. And if you've no such interest despite that its information would have been useful to you, the game, by readies the rut for you. Follow it to have access only to an increasingly narrow span of the game's combat content, replacing such with further social conflict.
For the later gaps, though, there's nothing. You can see all the mechanics symbols likely to be repurposed, but unless the concepts and habits necessary for that later content is centered upon and drawn attention to, however unintrusively, it will click for some --for whom Savage will be presented about as attractively as its sum of actual mechanics, novelty, etc., can be to that individual-- and not for others -- for whom that content will not be given a remotely attractive view.
So, yes, it does have much to do with inclusivity, in the same way that good pedagogical or instructional practices anywhere, even if not necessary for anyone and everyone, still benefit the given community, especially if it's often grouped as one.