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

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

Optimization · Pure Optimization
An open-world JRPG where build construction and art rotation planning win battles.
Portal leans Optimization (Pure Optimization); Xenoblade Chronicles leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
Xenoblade Chronicles
Positioning during auto-attack combat needs minimal dexterity
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.
Xenoblade Chronicles
Enemy AI runs fixed aggro and art rotations
Xenoblade Chronicles leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
Xenoblade Chronicles
Drop rates and unexplored zones add mild uncertainty
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.
Xenoblade Chronicles
Art rotations, gem crafting and party builds decide fights
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.