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 mystery about a fire lookout in a Wyoming forest.

Optimization · Light / Casual
Short narrative horror about a doomed freighter crew told in fractured time.
Firewatch leans Optimization (Light / Casual); Mouthwashing leans Optimization (Light / Casual).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Firewatch
Walking and radio dialogue only.
Mouthwashing
Walking and simple interactions
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.
Mouthwashing
No opposition; it is a story
Mouthwashing leans a little harder on variance, though the gap is small.
Firewatch
Minor environmental discoveries.
Mouthwashing
Narrative surprises only on first viewing
Mouthwashing leans a little harder on optimization, though the gap is small.
Firewatch
Few systems to optimize.
Mouthwashing
Light puzzles guide a fixed story
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.