Look, nobody is arguing that technically everything is scalable. But have you ever played a game on pc with zero loading times or a game where Ray Tracing is a core gameplay mechanic? SSD and RTX cards has been around for a long time but only with these next gen consoles, developers will be able to really take advantage of it.
Parity is a thing that developers have to develop around as they want to sell us a game that provides the same experience across all platforms, meaning the games have to hit certain performance targets on the lowest common denominator. Halo Infinite won't look like a blurry mess, chugging at 20fps on the Xbox One, it will likely be one of the best looking Xbox games to date running at a steady 30fps at 900p. It would have been a different story if MS said they're outsourcing the Xone version, and it would basically be a different game - like we've seen in the past with Forza. But that's different than making 1 game with scalable graphics settings that'll have the same geometry, ai, physics etc on all platforms.
Sony hasn't showed us a lot but just look at Ratchet & Clank. MS would never have made a Series X exclusive that uses the SSD as a core gameplay mechanic. Not because its technically impossible on Series X, but because 95% of the GP users - who don't have a NVME SSD - wouldn't be able to play it.