head to head
Neither is simply harder - they are hard in different places. Dragon Age: Inquisition demands more variance; Portal 2 demands more optimization.

Optimization · Pure Optimization
An action-RPG hybrid driven by crafting, specialization, and war-table routing.

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.
Dragon Age: Inquisition 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.
Dragon Age: Inquisition
Action-leaning combat, dodge timing matters
Portal 2
Portal placement requires some precision but timing is lenient.
Dragon Age: Inquisition leans a little harder on reads, though the gap is small.
Dragon Age: Inquisition
Scripted enemy behaviour
Portal 2
No opponent; puzzles are static.
Dragon Age: Inquisition leans clearly harder on variance.
Dragon Age: Inquisition
Some loot randomization
Portal 2
Puzzles are deterministic with no randomness.
Portal 2 leans clearly harder on optimization.
Dragon Age: Inquisition
Crafting, specialization, war table planning
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.