head to head
Neither is simply harder - they are hard in different places. Portal 2 demands more execution; Shin Megami Tensei: Nocturne demands more variance.

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

Optimization · Pure Optimization
Exploiting the press-turn system through demon fusion and weakness math.
Portal 2 leans Optimization (Pure Optimization); Shin Megami Tensei: Nocturne leans Optimization (Pure Optimization).
Portal 2 leans clearly harder on execution.
Portal 2
Portal placement requires some precision but timing is lenient.
Shin Megami Tensei: Nocturne
Turn-based menus carry zero dexterity 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.
Shin Megami Tensei: Nocturne
Brutal bosses still run fixed scripts
Shin Megami Tensei: Nocturne leans clearly harder on variance.
Portal 2
Puzzles are deterministic with no randomness.
Shin Megami Tensei: Nocturne
Unknown boss gimmicks and fusion luck sting first attempts
Portal 2 leans a little harder on optimization, though the gap is small.
Portal 2
Solving the puzzle's logic IS the entire game.
Shin Megami Tensei: Nocturne
Press-turn exploitation and fusion planning decide everything
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.