head to head
Neither is simply harder - they are hard in different places. Naughty Bear demands more variance; Portal 2 demands more optimization.

Optimization · Pure Optimization
Optimising terror combos against scripted victims to maximise a points score per level.

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.
Naughty Bear leans Optimization (Pure Optimization); Portal 2 leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Naughty Bear
Simple melee and chase inputs with low timing demands
Portal 2
Portal placement requires some precision but timing is lenient.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Naughty Bear
Victim bears run scripted panic routines, never modelling you
Portal 2
No opponent; puzzles are static.
Naughty Bear leans clearly harder on variance.
Naughty Bear
Bear patrols add mild unpredictability per attempt
Portal 2
Puzzles are deterministic with no randomness.
Portal 2 leans clearly harder on optimization.
Naughty Bear
Maximising scare-point combos per level is a solvable puzzle
Portal 2
Solving the puzzle's logic IS the entire game.
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.