head to head
Neither is simply harder - they are hard in different places. Portal demands more execution; The Temple of Elemental Evil demands more variance.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.

Optimization · Pure Optimization
Mastering faithful D&D 3.5 rules and party builds against dice-roll swing.
Portal leans Optimization (Pure Optimization); The Temple of Elemental Evil leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
The Temple of Elemental Evil
Turn-based clicks - hands never matter
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Portal
No adversary modeling player.
The Temple of Elemental Evil
Encounters run on D&D scripts, not adaptation
The Temple of Elemental Evil leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
The Temple of Elemental Evil
Dice rolls swing fights until builds overpower them
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Portal
Pure puzzle-solving optimization.
The Temple of Elemental Evil
Mastering 3.5e rules, builds and positioning is the 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.