Portal RTX is the kind of thing that absolutely destroys AMD on the marketing front. NV lets all cards run it, but the whole thing is coded for the RTX4xxx series and optimized a bit for the RTX3xxx series.
While I doubt the 6900XT would be blowing anyone away with its RT performance in the best of times, it is so underperforming here that I can only assume that NV not only didn't optimize for AMD cards (obviously) but might have actually even built in deliberate code to bottleneck AMD cards unrealistically.
Curiously, I wonder if we'll see an FSR2.0 .dll swap available for this game.
I think it's the same trick as with tessellation, excessive amounts of rays.
Yes, the RTX4 series is better for being able to process a greater number of rays. Games with RT will be faster on a RTX4 card, but on a game like this, it's just being used to "showcase" how faster RTX4 series can be, NOT to show how good the game can look with RT. They're just shooting as many rays the 4090 can process (actually above, the card can't reach 60fps). If you drop the number of rays and some bounces in half would make no difference, but then this would be just Portal with Raytracing, not a showcase for the 4090.
Because the RDNA 2 cards are still round Turing with some disadvantages of course it performs so bad.
This is stupid, RT is good indeed, but you just have to remember that some game for the current gen consoles exist and can deliver excellent RT with a fraction of that RT processing power to understand how stupid this is.
Unfortunately RT is still on that fase of developers using it badly instead of smartly.
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