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

Optimization · Light / Casual
A hidden-object detective adventure solved through clues and inventory puzzles.

Optimization · Light / Casual
A first-person mystery about a fire lookout in a Wyoming forest.
Art of Murder: Cards of Destiny leans Optimization (Light / Casual); Firewatch 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.
Art of Murder: Cards of Destiny
no reflex requirement, point-and-click
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.
Art of Murder: Cards of Destiny
no opponent to read
Firewatch
No adaptive opposition.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Art of Murder: Cards of Destiny
fixed clues, little randomness
Firewatch
Minor environmental discoveries.
Art of Murder: Cards of Destiny leans a little harder on optimization, though the gap is small.
Art of Murder: Cards of Destiny
logical deduction and inventory puzzle solving
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.