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.

Optimization · Light / Casual
A first-person mystery set in a snowed-in hotel, driven entirely by exploration and phone calls.
Firewatch leans Optimization (Light / Casual); The Suicide of Rachel Foster leans Optimization (Light / Casual).
Firewatch leans a little harder on execution, though the gap is small.
Firewatch
Walking and radio dialogue only.
The Suicide of Rachel Foster
Walking a hotel; no dexterity test.
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 Suicide of Rachel Foster
No opponent; a phone companion guides you.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Firewatch
Minor environmental discoveries.
The Suicide of Rachel Foster
Fixed mystery; nothing randomised.
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 Suicide of Rachel Foster
Light navigation and clue-following through the hotel.
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.