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

Optimization · Light / Casual
A first-person horror about exploring a haunted Prussian castle.

Optimization · Light / Casual
A first-person mystery about a fire lookout in a Wyoming forest.
Amnesia: The Dark Descent leans Optimization (Light / Casual); Firewatch leans Optimization (Light / Casual).
Amnesia: The Dark Descent leans a little harder on execution, though the gap is small.
Amnesia: The Dark Descent
Stealth and hiding, low demand.
Firewatch
Walking and radio dialogue only.
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.
Firewatch
No adaptive opposition.
Amnesia: The Dark Descent leans a little harder on variance, though the gap is small.
Amnesia: The Dark Descent
Minor encounter variation.
Firewatch
Minor environmental discoveries.
Amnesia: The Dark Descent leans a little harder on optimization, though the gap is small.
Amnesia: The Dark Descent
Oil and sanity management is shallow.
Firewatch
Few systems to optimize.
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.