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 first-person horror about exploring a haunted Prussian castle.

Variance · Light / Casual
Claustrophobic horror short about piloting a blind submarine through a blood ocean.
Amnesia: The Dark Descent leans Optimization (Light / Casual); Iron Lung leans Variance (Light / Casual).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Amnesia: The Dark Descent
Stealth and hiding, low demand.
Iron Lung
Slow submarine piloting by coordinates
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Amnesia: The Dark Descent
Monsters follow scripted patrols.
Iron Lung
The thing outside follows a script
Iron Lung leans a little harder on variance, though the gap is small.
Amnesia: The Dark Descent
Minor encounter variation.
Iron Lung
Blind navigation; you see only camera snapshots
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Amnesia: The Dark Descent
Oil and sanity management is shallow.
Iron Lung
Plotting waypoints on the paper map
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.