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
The original post-apocalyptic CRPG where character builds solve the wasteland.

Optimization · Pure Optimization
Optimising a strict social calendar and fusion economy against scripted dungeon combat.
Fallout leans Optimization (Pure Optimization); Persona 3 Portable 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.
Fallout
Turn-based, no dexterity
Persona 3 Portable
Menu-driven combat needs no physical skill
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout
No adaptive opposition
Persona 3 Portable
Shadows follow scripted weakness patterns, never adapt
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout
To-hit rolls and random encounters
Persona 3 Portable
Tartarus layouts and fusion results carry randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout
SPECIAL builds and quest routing are deeply solvable
Persona 3 Portable
Calendar scheduling and persona fusion form a solvable system
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.