Resolution is usually the most talked about, because it's easy to as advertise. Theres so much that can be configured that affects performance besides resolution.
Look at the "optimized xbox one x settings" for Rdr2 for PC per Digital foundry. Some of those settings are lower than the lowest settings available on PC, because Rockstar were able to scale to the hardware accordingly.
Per DF,
Changing Lighting Quality from Ultra -> Medium gave them a 14% performance increase. That's one setting alone.
Changing reflections from Ultra to their optimized X1 settings gave them between a 11 - 17% increase in performance.
Changing shadows from Ultra to their optimized X1 settings gave them a 7% increase in performance.
Theres are settings like anistrophic filtering and texture quality that barely change performance, with texture quality affecting vram usage, but when people talk about scalability in game development this is what they mean.