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

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

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Disco Elysium leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Disco Elysium
No mechanical inputs of consequence
Portal
Portal placement timing modest.
Disco Elysium leans a little harder on reads, though the gap is small.
Disco Elysium
Dialogue partners are scripted, not modeling you
Portal
No adversary modeling player.
Disco Elysium leans clearly harder on variance.
Disco Elysium
Skill checks roll dice with hidden modifiers
Portal
Deterministic chambers; no randomness.
Portal leans a little harder on optimization, though the gap is small.
Disco Elysium
Build skills and route choices to pass checks
Portal
Pure puzzle-solving optimization.
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.