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

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

Optimization · Pure Optimization
Tests exploiting stackable upgrade systems in a janky open-world RPG.
Portal 2 leans Optimization (Pure Optimization); Two Worlds 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.
Two Worlds
Clunky combat asks little beyond basic timing
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.
Two Worlds
Enemies are simple scripted aggro
Two Worlds leans clearly harder on variance.
Portal 2
Puzzles are deterministic with no randomness.
Two Worlds
Loot drops and unexplored map hold mild hidden information
Portal 2 leans clearly harder on optimization.
Portal 2
Solving the puzzle's logic IS the entire game.
Two Worlds
Stackable item enchanting and builds break the game open
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.