So frame rate doubles, but resolution drops by around 80%?
I think the issue here is that the games do not actually trigger their dynamic resolution in this due to them being programmed in a way that they only start to drop after the framerate goes below 60fps
so Titanfall 2 would basically try to run at up to 6K resolution on Series X (yes the dynamic res window goes that high in it) and only if it would drop down to 59fps would the engine ever start to drop the resolution to sustain a stable performance. as a result the game would most likely run only slightly above 60fps because it would almost always run at above 4K or at 4K
we can see that the dynamic res doesn't trigger in the instances where the Series S drops way below 120fps but the dynamic res does not drop whatsoever.
if these games ran at a locked 4K60 on One X they would run at around 4k120 on Series X, but they don't. all these games drop down significantly below 4K on One X when stressed, but at 120fps they couldn't use the dynamic res to stabilize fps.
Titanfall 2 can theoretically run at 6K60fps on One X, and according to Respawn it actually hits that res in very rare undemanding scenes on undemanding maps. but it of course actually runs more in the neighborhood of ~1500p in normal gameplay scenarios
same, to a lesser degree, with Battlefied 1 and V, they can run at 4K60 but they usually don't and use the dynamic res in really stressful scenes to keep that framerate up, so they can go down way hard at times.
so they just run the games in One S mode where the dynamic res has a way lower upper boundary. the developers would need to patch the games specifically to target 120fps with their dynamic res in order to fix this.