head to head
Neither is simply harder - they are hard in different places. Portal 2 demands more optimization; The Witcher: Enhanced Edition Director's Cut demands more variance.

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

Optimization · Pure Optimization
Preparation-driven RPG combat where potions, builds and monster knowledge beat reflexes.
Portal 2 leans Optimization (Pure Optimization); The Witcher: Enhanced Edition Director's Cut 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.
Portal 2
Portal placement requires some precision but timing is lenient.
The Witcher: Enhanced Edition Director's Cut
Rhythm-click combat is timing-light and forgiving
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.
The Witcher: Enhanced Edition Director's Cut
Enemies follow fixed behaviours, nothing adapts to you
The Witcher: Enhanced Edition Director's Cut leans clearly harder on variance.
Portal 2
Puzzles are deterministic with no randomness.
The Witcher: Enhanced Edition Director's Cut
Quest outcomes are scripted-but-unknown on a first playthrough
Portal 2 leans clearly harder on optimization.
Portal 2
Solving the puzzle's logic IS the entire game.
The Witcher: Enhanced Edition Director's Cut
Alchemy prep, signs and talent builds decide every fight
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.