BocoDragon
or, How I Learned to Stop Worrying and Realize This Assgrab is Delicious
I'd say it's more part of a global postmodern condition. A lot of our media mixes deep complex issues with an ironic self-awareness, the defining trait of postmodernism, and there's no form of media that's more inherently postmodern than videogames. It's probably more obvious in anime or games as they are relatively newer artforms, but a lot of our most prominent contemporary media balances serious issues with goofiness from Pynchon to Star Wars, for two examples.
I see what you're saying and I find that interesting to wrap my mind around.... but I think it's incorrect.
FFXV is not a product of self-reflective Millennial irony. It's not from the same pool of conscious irony, remixing of ideas and self-conscious in-jokes as stuff like Deadpool, Undertale or The Force Awakens (i.e. "What if there were a Vader fanboy who had issues with the previous generation?").
It's actually kind of regressive in the Japanese context. It's another anime-style property that doesn't think to divide between serious/goofy or modern/classic, because it reflects a lack of division between these things in Japanese pop culture mediums. That we think they are inappropriate juxtapositions is our bias coming from a different cultural tradition.
When you have a jRPG that consciously makes fun of jRPGs or anime, then I will agree with you that it has been inducted into the ironic too-clever, post-modern Millennial hall of fame.