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

Optimization · Pure Optimization
Generous team-building optimisation against fixed Kalos trainers.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Pokémon Y leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Pokémon Y
Turn-based menus have no physical ceiling
Portal
Portal placement timing modest.
Pokémon Y leans a little harder on reads, though the gap is small.
Pokémon Y
Campaign trainers are scripted; online play is a separate pursuit
Portal
No adversary modeling player.
Pokémon Y leans clearly harder on variance.
Pokémon Y
Encounters and rolls add bounded, mappable 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.
Pokémon Y
Mega evolutions and EV tools make optimisation the core
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.