head to head
Neither is simply harder - they are hard in different places. Portal 2 demands more optimization; Vampire: The Masquerade - Bloodlines demands more variance.

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

Optimization · Pure Optimization
A cult-classic vampire RPG won by discipline choice and skill-check routing.
Portal 2 leans Optimization (Pure Optimization); Vampire: The Masquerade - Bloodlines 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.
Vampire: The Masquerade - Bloodlines
Janky hybrid combat, low demand
Vampire: The Masquerade - Bloodlines leans a little harder on reads, though the gap is small.
Portal 2
No opponent; puzzles are static.
Vampire: The Masquerade - Bloodlines
Scripted NPCs
Vampire: The Masquerade - Bloodlines leans clearly harder on variance.
Portal 2
Puzzles are deterministic with no randomness.
Vampire: The Masquerade - Bloodlines
Hidden dice under skill checks
Portal 2 leans clearly harder on optimization.
Portal 2
Solving the puzzle's logic IS the entire game.
Vampire: The Masquerade - Bloodlines
Discipline, feeding, build routing central
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.