head to head
Portal 2 asks more than Steins;Gate, and the gap is optimization.

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

Optimization · Pure Optimization
A time-travel mystery where finding the correct sequence of phone interventions is the puzzle.
Portal 2 leans Optimization (Pure Optimization); Steins;Gate leans Optimization (Pure Optimization).
Portal 2 leans clearly harder on execution.
Portal 2
Portal placement requires some precision but timing is lenient.
Steins;Gate
Pure reading; phone choices are the only input
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.
Steins;Gate
No opponent; timeline branches are fixed
Steins;Gate leans a little harder on variance, though the gap is small.
Portal 2
Puzzles are deterministic with no randomness.
Steins;Gate
Phone trigger timing hides branch conditions until discovered
Portal 2 leans clearly harder on optimization.
Portal 2
Solving the puzzle's logic IS the entire game.
Steins;Gate
Mapping exact phone responses to unlock the True End is solvable
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.