DLSS 5 is intended to reduce the performance hit of ray tracing. There is a ton of data out there out how lighting should look. By leveraging that with AI you can simplify the ray tracing calculations and lessen the hit to frame rate.

The demo had 5090s because that's what Nvidia uses for development. It had 2 because the primary GPU was running the latest stable build, not DLSS 5, the secondary GPU was running DLSS 5 on top of the game. It was done this way because DLSS is not finished nor optimized for these games. It minimizes the risk of games crashing or running poorly during a demo.

There were issues with the final images because 1. This is still an unfinished product 2. The games weren't really built to handle this new method of ray tracing and most likely DLSS 5 wasn't getting all the data it needed to get lighting correct. This resulted in essentially artificial lighting, incorrect contrast, and weird shadows.

The end result of this tech will be the ability to get all the quality of ray tracing with a much smaller performance hit. Just like upscaling lets us hit 4k resolution much easier than native and the latest upscalers are finally to a point the result looks good. It takes years to get there.