head to head
Neither is simply harder - they are hard in different places. Indiana Jones and the Fate of Atlantis demands more variance; Portal demands more execution.

Optimization · Pure Optimization
LucasArts adventure sending Indy down three routes toward Atlantis.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Indiana Jones and the Fate of Atlantis leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Indiana Jones and the Fate of Atlantis
Pointing and clicking, light fistfight option
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 Fate of Atlantis
No adaptive opposition
Portal
No adversary modeling player.
Indiana Jones and the Fate of Atlantis leans clearly harder on variance.
Indiana Jones and the Fate of Atlantis
Solutions hidden until reasoned out
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 Fate of Atlantis
Three-path puzzle chains reward 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.