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 mystery about a fire lookout in a Wyoming forest.

Variance · Light / Casual
An exploration of narrative branches that deliberately tests nothing.
Firewatch leans Optimization (Light / Casual); The Stanley Parable leans Variance (Light / Casual).
Firewatch leans a little harder on execution, though the gap is small.
Firewatch
Walking and radio dialogue only.
The Stanley Parable
Walking is the only input
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Firewatch
No adaptive opposition.
The Stanley Parable
The narrator is a script, however much he pretends otherwise
The Stanley Parable leans a little harder on variance, though the gap is small.
Firewatch
Minor environmental discoveries.
The Stanley Parable
Endings are hidden information until you wander into them
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Firewatch
Few systems to optimize.
The Stanley Parable
Finding all branches is a trivial checklist
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.