head to head
Neither is simply harder - they are hard in different places. Portal 2 demands more execution; The Temple of Elemental Evil demands more variance.

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.

Optimization · Pure Optimization
Mastering faithful D&D 3.5 rules and party builds against dice-roll swing.
Portal 2 leans Optimization (Pure Optimization); The Temple of Elemental Evil leans Optimization (Pure Optimization).
Portal 2 leans clearly harder on execution.
Portal 2
Portal placement requires some precision but timing is lenient.
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 2
No opponent; puzzles are static.
The Temple of Elemental Evil
Encounters run on D&D scripts, not adaptation
The Temple of Elemental Evil leans clearly harder on variance.
Portal 2
Puzzles are deterministic with no randomness.
The Temple of Elemental Evil
Dice rolls swing fights until builds overpower them
Portal 2 leans a little harder on optimization, though the gap is small.
Portal 2
Solving the puzzle's logic IS the entire game.
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.