head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Optimization · Light / Casual
A first-person mystery about a fire lookout in a Wyoming forest.

Optimization · Light / Casual
A cozy sandbox about a cat causing mischief while finding its way home.
Firewatch leans Optimization (Light / Casual); Little Kitty, Big City 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.
Little Kitty, Big City
Gentle climbing and pouncing, no fail states
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.
Little Kitty, Big City
No opponents
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.
Little Kitty, Big City
Fixed sandbox neighborhood
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.
Little Kitty, Big City
Light quest checklist and shiny collecting
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.