The quote from Nvidia was meant to show that all rtx cards are supported where possible and they won't necessarily drop the improvements as you suggested . If dlss3 could run well or not on ada we just don't know, just as we don't know why turing didn't received the upscaling for video playback - aka dlss for video.
Moreover, the test was to show that the card cab still perform decently after all these years and hasn't been gimped in preparation for Ada's launch.
SER, from my understanding, is a specific optimization for Ada. Doesn't mean you don't optimize your game, just that you can do a bit extra for a very THIN slice of potential gamers. For that small number of potential customers, I don't see a lot of studios line up to show the middle finger to the rest of the market.
Performance mode is not weakest, that's ultra performance. Performance is decent now compared to where it was at launch and I think is quite better than quality mode in crysis remaster
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