I'm sure you're right about this. Probably the framerate bounces all over the place which feels much worse than simply locking it to 30fps and having a consistent experience. I think a PC has the potential to simply brute force it into 60fps, but an Xbox simply cannot. Which is probably fine. The game is said to run at 4k and 1440p depending on which Xbox you have, and for a game like this where exploration is going to play a big role, those visuals will do a lot of silent storytelling.

I would rather walk over a hill and see an incredible alien sunset on some moon, than have more frames, especially if those frames are bouncing around between 60 and 40 and going over that hill stutters and jerks spoiling the immersion.