IMHO there should be much more WIP material like this in the public, published by the game developers themselves. Too many people think that games just spring into existance, without a clear idea how game development actually works.
> a huge part of the appeal of games is the illusion there's more than meets the eye. Most gamers want to suspend their disbelief and let their imagination run rampant
This is complete nonsense.
I guess it's a bit like watching the BTS of something like the LotR trilogy. When you get to see all the orcs in full makeup just goofing around with the rest of the film crew, it means when you see them later in the real movie, you can't help but be reminded they're just people in great makeup. Keeping up that illusion in game dev must be enormously important.
(Whereas small/solo indie devs often show in-development work, because having anything seen that might interest future players is much more important to them)
EDIT: case in point, even here we already have comments wondering what mistakes Rockstar made because this random development footage, likely years before release, doesn't look that much better than GTA V.
I can safely predict that this leak will have approximately zero impact on the actual sales of GTA VI however.