But buying an RTX 5090 isn't going to turn GTA into a photorealistic game, and by the time a GTA with that level of graphics is released, many cheaper graphics cards will have approaching 5090 performance at far less power. My 6700 XT significantly outperforms a Titan X, the first $1000 card (released ten years ago, so equivalent to $1300 today according to some).
Somebody buying a 5090 is likely only going to see improvements if they measure the benchmark numbers. There might be games only playable at 4K/Ultra/RT on a 5090, but these days turning down the details a few notches only makes a difference when examining static screenshots side by side. (Even the ray-tracing stuff is too often a
minimal improvement.) I bust out Mankind Divided again recently, a 2016 game that I could play perfectly well with my old R9 290 with some of the details turned down. Now I'm playing it for the first time with everything turned to the max but I can't say I notice any improvement.
Then again, that doesn't make it a problem for the graphics cards companies if they can sell the things. An $80,000 BMW might be enough, but Bugatti still easily sold out of the Chiron.