That's not the same thing. The Base Xbox One is not going to run in the same solar system as 60fps, so they've capped it at 30fps, and it will dip constantly. What was the last 60fps FPS title that you played with an option to voluntary halve the framerate, significantly increase input latency, and so on? FPS developers are obsessed with trying to reduce input latency as much as possible. Basically nobody wants to release 30fps FPS titles, but sometimes they have to because consoles are kinda underpowered. Developers are motivated to add 30fps caps is to prevent uneven frame times on hardware that doesn't come close to 60fps. Doom 2016 runs at 60fps. So does Wolfenstein. It doesn't have a 30fps mode for the "input latency is awesome" demographic. It's never been a consideration in the FPS genre because of how paramount input responsiveness is. The Switch versions of those games run at 30fps because they have no choice.
Remember that the Xbox One S and the Xbox One X are fundamentally different consoles.
edit: Remember Prey and its kinda dogshit input latency on consoles? If Arkane had been able to get that game running at 60fps, allowing users to run at 30fps would have been nonsensical. The X version of Rage 2 is going to be a dramatically better game than the Xbox One S version. The S version is going to feel like treacle.
Forza Horizon 4 has the option and both modes are awesome in their own ways. The majority of people that play Rage 2 on console will play it on a base console...