head to head
Neither is simply harder - they are hard in different places. Disco Elysium demands more variance; Portal 2 demands more execution.

Optimization · Pure Optimization
A dialogue RPG resolved by stat builds against dice checks.

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.
Disco Elysium leans Optimization (Pure Optimization); Portal 2 leans Optimization (Pure Optimization).
Portal 2 leans clearly harder on execution.
Disco Elysium
No mechanical inputs of consequence
Portal 2
Portal placement requires some precision but timing is lenient.
Disco Elysium leans a little harder on reads, though the gap is small.
Disco Elysium
Dialogue partners are scripted, not modeling you
Portal 2
No opponent; puzzles are static.
Disco Elysium leans clearly harder on variance.
Disco Elysium
Skill checks roll dice with hidden modifiers
Portal 2
Puzzles are deterministic with no randomness.
Portal 2 leans clearly harder on optimization.
Disco Elysium
Build skills and route choices to pass checks
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.