We knew that the Xbox Series S wasn’t going to be a powerhouse console in comparison to the Xbox Series X and the PS5, but we were still expecting an upgrade over the current (now previous) generation of Xbox One and PlayStation 4. Instead, it’s starting to look like the Xbox Series S might be more of a sidegrade if you already own those consoles.
Digital Foundry just did a big comparison with one of the few next-gen games to release for all three consoles on their respective launch days. Assassin's Creed Valhalla is the latest entry into the franchise that was designed to play nice with everyone. Even though it's a third-party game, we're still expecting to see some pretty impressive numbers being put up by the Xbox Series X and PS5.
And it became pretty clear right off the bat that both consoles were a league better than the Xbox Series S. The differences in gameplay between the PS5/Xbox Series X and the Xbox Series S were stark, with drastically lower frame rate, draw distance, and resolutions on textures and overall gameplay.
The Xbox Series S was advertised with a target resolution of 1440p, but it looks like Assassin's Creed Valhalla's dynamic scaling puts resolution much closer to 1080p during heavy action. Digital Foundry reports dynamic resolutions between 1108 and 1656p--not a problem if you're playing on an older 1080p television, but definitely an issue if you've got an ultra-high-definition TV or monitor.
Performance on the Xbox Series S was honestly more on par with the Xbox One X or PS4 Pro. Frame rates were a solid 30fps, and texture quality was higher, but otherwise, there wasn't much reason to consider the Xbox Series S an upgrade.
Between the PS5 and the Xbox Series X, the PS5 came out the clear winner with faster load times, higher average framerates, and far less screen tearing than on the Xbox Series X. There was also a weird issue where the Xbox version of Valhalla doesn't render cutscenes properly, making the camera appear jittery and stuttery. That's apparently a bug that will hopefully get fixed later.
Source: Digital Foundry