head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is variance, and it is a single point.

Optimization · Pure Optimization
Sci-fi thriller played as the station AI solving its own crisis.

Optimization · Pure Optimization
A story-driven survival adventure alone on a hostile alien planet.
Observation leans Optimization (Pure Optimization); The Solus Project leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Observation
Camera control and interface manipulation
The Solus Project
Exploration platforming with mild precision needs
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Observation
Events are fully authored
The Solus Project
No adaptive entities, only environment
The Solus Project leans a little harder on variance, though the gap is small.
Observation
Mystery unknown until uncovered
The Solus Project
Alien caves hidden until explored, single playthrough mostly
The Solus Project leans a little harder on optimization, though the gap is small.
Observation
Systems puzzles and station schematics solving
The Solus Project
Managing temperature, hunger, and route planning drives survival
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.