head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Optimization · Pure Optimization
Optimising a strict social calendar and fusion economy against scripted dungeon combat.

Optimization · Pure Optimization
Mastering faithful D&D 3.5 rules and party builds against dice-roll swing.
Persona 3 Portable leans Optimization (Pure Optimization); The Temple of Elemental Evil leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Persona 3 Portable
Menu-driven combat needs no physical skill
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.
Persona 3 Portable
Shadows follow scripted weakness patterns, never adapt
The Temple of Elemental Evil
Encounters run on D&D scripts, not adaptation
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Persona 3 Portable
Tartarus layouts and fusion results carry 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.
Persona 3 Portable
Calendar scheduling and persona fusion form a solvable system
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.