head to head
Neither is simply harder - they are hard in different places. Final Fantasy X-2 demands more variance; Portal demands more execution.

Optimization · Pure Optimization
The poppy direct sequel to FFX where Yuna's trio swaps job dresspheres mid-battle across Spira.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Final Fantasy X-2 leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Final Fantasy X-2
Active Time Battle rewards quick menuing slightly.
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.
Final Fantasy X-2
All enemies follow scripted AI routines.
Portal
No adversary modeling player.
Final Fantasy X-2 leans clearly harder on variance.
Final Fantasy X-2
Drop rates and unknown encounters until mapped.
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.
Final Fantasy X-2
Dressphere builds, garment grids, and completion routing dominate.
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.