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

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.

Optimization · Pure Optimization
One of the deepest classic JRPGs, where party optimization and precise recruitment routing unlock its full richness.
Portal leans Optimization (Pure Optimization); Suikoden II leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
Suikoden II
Menu combat; duel minigame has mild timing
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Portal
No adversary modeling player.
Suikoden II
All enemies scripted; no player-modeling AI
Suikoden II leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
Suikoden II
Rune drop RNG and recruitment trigger timing add light variance
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Portal
Pure puzzle-solving optimization.
Suikoden II
Party comp, rune combos, and duel answer memorization are solvable
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.