The reward is the challenge, and to test your abilities as a player. A gear reward would be nice (as a progression alternative to savage), but it is far from required. Players—especially Final Fantasy players, given the lack of reward from super bosses in the single-player installments—do not need any other carrot.
You do realize that doing a dungeon undersized and / or undergeared does not make it harder? The boss and trash damage is still the same, as is health and stats. For players who do not suck (avoids the avoidable mechanics) doing it in such a way simply makes it longer, not harder. On the other hand, if you scale the dungeons, then everything hits harder; so those boss attacks that the healer ignores now must be attended to, making their job much more difficult.
As for tomestones versus gear, I'd rather be gear farming (like the extreme primals) where I know that every kill I come closer to what I want, instead of farming easy content to cap out on a currency that I'll get one thing 2-3 weeks from now, regardless of how well I play.
The only people who would benefit from scaling difficulty dungeons in XIV are recent WoW players? So how do players playing WoW benefit at all from something new in XIV?
Your ridiculousness aside, no, it's not just "recent WoW players" benefit from it. Players (in XIV) who are looking for a hard challenge (there is a reason we're getting Super Savage / Ultimate Series) have yet another outlet for it. I mean, they could still attach creation tomestones to it (more than what the normal difficulty gives, obviously), and I would love to do a much harder version for a greater reward.
To you I repeat this firmly: just because WoW has a system does not mean it is a terribly idea to be used outside of WoW. I'm an ex-WoW player, and there are several things I never want to see from WoW in this game, but that does not mean I'll willfully ignore the real positive systems that could be of great value here.
So just stop the hate.