head to head
Neither is simply harder - they are hard in different places. Persona 5 demands more variance; Portal demands more execution.

Optimization · Pure Optimization
Stylish JRPG where phantom thieves steal hearts on a tightly optimized school calendar.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Persona 5 leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Persona 5
Stylish menus, not reflexes
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.
Persona 5
Palace enemies use fixed weaknesses
Portal
No adversary modeling player.
Persona 5 leans clearly harder on variance.
Persona 5
Fusion alerts and negotiation rolls
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.
Persona 5
Confidant calendar routing and baton-pass weakness chains
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.