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

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

Optimization · Pure Optimization
A tactical RPG testing positioning and turn prediction on a grid battlefield.
Portal leans Optimization (Pure Optimization); Vandal Hearts II leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
Vandal Hearts II
Simultaneous-turn combat has no twitch input
Vandal Hearts II leans clearly harder on reads.
Portal
No adversary modeling player.
Vandal Hearts II
Predicting AI move order matters but follows scripts
Vandal Hearts II leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
Vandal Hearts II
Hit chances add bounded randomness
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.
Vandal Hearts II
Unit positioning, builds and the prediction system win battles
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.