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

Optimization · Pure Optimization
Type-matchup math and team construction across a scripted Sinnoh campaign.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Pokémon Pearl Version leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Pokémon Pearl Version
Menu-driven battles need no dexterity
Portal
Portal placement timing modest.
Pokémon Pearl Version leans a little harder on reads, though the gap is small.
Pokémon Pearl Version
Gym leaders are scripted; online battles are optional
Portal
No adversary modeling player.
Pokémon Pearl Version leans clearly harder on variance.
Pokémon Pearl Version
Encounter tables and battle rolls are mappable RNG
Portal
Deterministic chambers; no randomness.
Portal leans a little harder on optimization, though the gap is small.
Pokémon Pearl Version
Team building and type matchups are the solvable 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.