head to head
Subnautica asks more than Portal 2, and the gap is variance.

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.

Optimization · Pure Optimization
An underwater survival game won by methodical tech progression.
Portal 2 leans Optimization (Pure Optimization); Subnautica leans Optimization (Pure Optimization).
Portal 2 leans a little harder on execution, though the gap is small.
Portal 2
Portal placement requires some precision but timing is lenient.
Subnautica
Movement is slow; no precision demands.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Portal 2
No opponent; puzzles are static.
Subnautica
Creatures follow scripted patrols; no adaptation.
Subnautica leans clearly harder on variance.
Portal 2
Puzzles are deterministic with no randomness.
Subnautica
Resource node placement mildly randomized.
Portal 2 leans a little harder on optimization, though the gap is small.
Portal 2
Solving the puzzle's logic IS the entire game.
Subnautica
Tech progression and base routing solve the ocean.
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.