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 · Light / Casual
A gorgeous first-person mystery about piecing together a boy's disappearance.

Optimization · Systems & Chaos
A wordless surreal exploration game about wandering a sleeping girl's dreamscapes.
The Vanishing of Ethan Carter leans Optimization (Light / Casual); Yume Nikki leans Optimization (Systems & Chaos).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
The Vanishing of Ethan Carter
Walking and looking, nothing more
Yume Nikki
Just walking, no challenge on inputs
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
The Vanishing of Ethan Carter
No opponent
Yume Nikki
No opponent of any kind
Yume Nikki leans a little harder on variance, though the gap is small.
The Vanishing of Ethan Carter
The mystery is hidden only until discovered
Yume Nikki
Random events and obscure unknown triggers
Yume Nikki leans a little harder on optimization, though the gap is small.
The Vanishing of Ethan Carter
Reconstructing event sequences is light deduction
Yume Nikki
Mapping the dream worlds to find 24 effects
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.