head to head
100 Aliens Cats asks more than Firewatch, and the gap is variance.

Variance · Light / Casual
A relaxing hidden-object game finding 100 cats in alien scenes.

Optimization · Light / Casual
A first-person mystery about a fire lookout in a Wyoming forest.
100 Aliens Cats leans Variance (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.
100 Aliens Cats
Pointing and clicking needs no dexterity
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.
100 Aliens Cats
Solo hidden-object game with no opponent
Firewatch
No adaptive opposition.
100 Aliens Cats leans clearly harder on variance.
100 Aliens Cats
Cat positions are hidden until found
Firewatch
Minor environmental discoveries.
100 Aliens Cats leans a little harder on optimization, though the gap is small.
100 Aliens Cats
Methodical searching speeds completion
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.