The main advantage of Space Marine 2 is optimization: Swarm handles even scenes with dozens and hundreds of enemies on screen perfectly. In this regard, the new Gears of War is inferior to Saber Interactive's shooter.
In the Realistic GameZ video, they also compared textures, environmental interaction, and physics. Gears of War: E-Day shows decent results, although water simulation seems to be better implemented in Space Marine 2.
Opinions on which game looks better will surely be divided. Both demonstrate a high level of graphics on PC and consoles.
At the same time, Gears of War: E-Day is capable of delivering a stable 60 FPS even on Xbox Series S, which is a significant achievement for a game on Unreal Engine 5. A separate video also showed how much the series' graphics have improved since Gears 5, which still impresses with its visuals.