Just keep note that we've seen barely anything of FFXV. What was being shown of FFXV is prior to the demo and the theme of friendship between guys.
If you haven't realized the 'dark' tones you are thinking of are still present in FFXV but not emphasised in SE's promotion and adverts thanks to some of the hints shown within recent footage and even the demo itself. For example, take Noctis & the gang's clothing. Colored black, some with skull patterns etc.
It's hinted that the theme still exists within the game, just hasn't been fully fleshed out yet. It will though. A theme as important as what was main in Versus XIII will have to play a huge role for FFXV.
I wouldn't really say that their sartorial designs falls into this category, per se. A black outfit doesn't necessarily set a tone for the environment they're in.
I'm still aware of how much we've /actually/ seen in relation to the project as a whole, but just from what I've seen, it's still pretty clear that there's been a change of atmosphere. (Like just look at how Noctis was characterized in Versus XIII trailers to how he is now.)
Way too much is still up in the air though, hopefully after Duscae 2.0, we can see more of what the game has to offer.
The demo's ending is an enough conformation that the game still have versus's dark tone.
I'll have to look at it again.
EDIT: Just did, I guess you guys are right. I suppose a lot of my apprehension is just in that it's been so many months of only Duscae that it's hard to not see the game represented in only this way lol.