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

Optimization · Pure Optimization
A classic-styled JRPG whose brave/default system turns turns themselves into a resource.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Bravely Default leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Bravely Default
Turn-based menus; no physical demands
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.
Bravely Default
Bosses follow fixed scripts
Portal
No adversary modeling player.
Bravely Default leans clearly harder on variance.
Bravely Default
Minor drop and encounter randomness
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.
Bravely Default
Job combos and brave/default economy are deeply solvable
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.