head to head
Neither is simply harder - they are hard in different places. Indiana Jones and the Last Crusade: The Graphic Adventure demands more variance; Portal demands more execution.

Optimization · Pure Optimization
LucasArts adventure retracing the film's hunt for the Holy Grail.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Indiana Jones and the Last Crusade: The Graphic Adventure leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Indiana Jones and the Last Crusade: The Graphic Adventure
Clicks plus optional simple fisticuffs
Portal
Portal placement timing modest.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Indiana Jones and the Last Crusade: The Graphic Adventure
Guards follow fixed logic
Portal
No adversary modeling player.
Indiana Jones and the Last Crusade: The Graphic Adventure leans clearly harder on variance.
Indiana Jones and the Last Crusade: The Graphic Adventure
Puzzle answers hidden on first play
Portal
Deterministic chambers; no randomness.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Indiana Jones and the Last Crusade: The Graphic Adventure
Dialogue routes and Grail-lore deduction
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.