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

Optimization · Pure Optimization
Team building and type-matchup optimization through a scripted island campaign.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Pokémon Moon leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Pokémon Moon
Turn-based menus require no dexterity
Portal
Portal placement timing modest.
Pokémon Moon leans a little harder on reads, though the gap is small.
Pokémon Moon
Scripted trials and trainers; competitive play is a niche mode
Portal
No adversary modeling player.
Pokémon Moon leans clearly harder on variance.
Pokémon Moon
Encounter tables, catch rolls and crits are mappable RNG
Portal
Deterministic chambers; no randomness.
Portal leans a little harder on optimization, though the gap is small.
Pokémon Moon
Team composition and type math 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.