They did the same with Bravely Default if you remember correctly, it also received little advertisement, was a new IP, and was actually published by Nintendo because SE had so little faith in it. Squenix doesn't ever give advertisement to anything that they don't believe is going to be a surefire hit.
Well to be fair, a lot of this content is DLC nonsense, so I wouldn't actually call it "core design". The Open World aspect is simply one element of the design and something RPGs have been utilizing for years before this game came out, so again, I don't necessarily feel this is SE moving away from "what an RPG is".And now they're transitioning away from the series even being an action-RPG. WTF even is Final Fantasy now? It's barely an RPG at all. From what I can tell, Square is just looking at everything popular, shoving it all in a blender, and tossing it out, while weakening the RPG aspects that are the core of the series the entire way. "Oh, Forza is a popular franchise, let's shove a car into it and make it a driving game." "Oh, people love open world games, let's make it open world." "Oh, people like VR, let's make a...uh, VR fishing game!" And, of course, the most recent "oh, people love multiplayer, let's add in multiplayer options".
They're not "experimenting" with the core design. They've discarded it. This isn't Final Fantasy anymore. I don't know WTF it is. I don't think SQUARE knows WTF it is. They're just sitting there with their dartboard of popular ideas, hoping to find the one that will work.
Driving around in a car is something that VIII had back on the PS1 and even required fuel to utilize. Even then, I would argue the car aspect (well until the silly off road DLC anyway) was designed to be very different from an actual driving game and frankly, I felt it was one of the better implemented ideas considering the biggest part of it's appeal is listening to the party banter and unlocking some of Prompto's photo quests.
I feel at best, one can argue that FFXV is certainly more modern WRPG than JRPG by design, that's pretty undeniable, but I would still say it's an RPG as it has more of the fundamental elements of the genre there which is a bit more than I can say about a certain previous entry... At the same time, I can agree that this design choice most likely alienated a certain part of the older fanbase, but again, Kitase doesn't make games for us. He's told us to move on and let the younger generation like FF instead.
I can't logically blame Kitase for adapting this approach either because it's easier to build a series on trends to appeal to a new generation than try to appeal to what is ultimately an unpleasible older fanbase. FF fans are the Trekkies of video games who all cut their teeth on the series from very different games. You can't possibly appeal to everyone without pissing someone off. It's easy to say "just make them like they were when they were good" but you ask fans when the series was "good" and you'll likely get a different response. We can go by sales so basically make every game like VII and X but I personally don't like those games and have several issues with both of their designs, so how is this fair for someone like me? See what I mean? We're too jaded, so why appeal to us when their name recognition almost guarantees that some new person will eventually check them out and become a new fan? I'm not saying SE doesn't like us aold fans, and haven't tried to appeal to us before, but again, we're all from very different generations of gaming with different needs and likes, appealing to us is always going to be an uphill battle and SE doesn't need to sacrifice their main franchise to do that when they can simply fund smaller projects to do so.
P5 showed a turn base game can still be financially successful, but that simply means SE still has that option, they don't have to follow because XV itself was also pretty damn successful itself, so P5's success didn't prove that one battle mechanic is superior to the other, it simply means the market is receptive to older design, but it only means SE has options, it doesn't mean they can't make up whatever system they want. It would have been a very different story if XV flopped and P5 was a success, but that might have also spelled bigger issues for Final Fantasy in general.