That demo was playable by the public on both PS5 and PC at the Konami TGS '24 booth. It wouldn't make much sense for something to be downgraded which is already running well on real hardware.
Worst case scenario would be that the demo was really running on PCs with a DualSense plugged in and the PS5 version ends up being downgraded since the new trailer says it was captured on a PS5 Pro.
But I just don't see any downgrade. The intro shots have a lot of depth of field so you can't really judge much from them. The shots we can compare that are as like-for-like as possible look the same:
1 year ago (Official Trailer #1):
Now:
Same color grading, texture detail, model quality etc.
1 year ago (Official Trailer #1):
Now:
Everything looks the same to me. Models, lighting, same washed out fog effect obscuring the distant shadows, the raised black levels. These shots could follow each other in the same trailer and would not look out of place.
1.5 years ago (First In-Engine Look trailer):
Now:
Some differences in color grading but water effects and textures are the same.
1.5 years ago (First In-Engine Look trailer):
Now:
Focus on the texture details, look at the brick walls - basically the same.
Screenshot from 4 months ago:
Now:
Even with all the Youtube compression you see it looks the exact same.
1.5 years ago (First In-Engine Look trailer):
Now:
Showing vegetation looks as good and the water drop effect is still in.
This shot looks as good as any environmental shot they've previously shown:
And i'll throw this shot in from the first official trailer one year ago, showing the game has always looked visually inconsistent:
GTA6 naysayers will all be proven wrong as soon as the gameplay trailer drops, just like they were proven wrong with GTAV and RDR2.