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 branching visual novel that tests little beyond exploring choice routes.

Optimization · Light / Casual
A first-person mystery about a fire lookout in a Wyoming forest.
Everlasting Summer leans Optimization (Light / Casual); Firewatch leans Optimization (Light / Casual).
Firewatch leans a little harder on execution, though the gap is small.
Everlasting Summer
Reading and clicking choices, nothing physical
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.
Everlasting Summer
No opponent - characters follow fixed branching scripts
Firewatch
No adaptive opposition.
Everlasting Summer leans a little harder on variance, though the gap is small.
Everlasting Summer
Route outcomes are hidden only until first playthroughs
Firewatch
Minor environmental discoveries.
Everlasting Summer leans a little harder on optimization, though the gap is small.
Everlasting Summer
Mapping choice branches to endings is trivially solvable
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.