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

Optimization · Pure Optimization
Solvable type-matchup planning across two regions of fixed trainers.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Pokémon Silver Version leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Pokémon Silver Version
Turn-based menus need no dexterity
Portal
Portal placement timing modest.
Pokémon Silver Version leans a little harder on reads, though the gap is small.
Pokémon Silver Version
Scripted trainers never adapt; link battles are a niche exception
Portal
No adversary modeling player.
Pokémon Silver Version leans clearly harder on variance.
Pokémon Silver Version
Encounters, crits and catch rolls are bounded RNG
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 Silver Version
Type coverage and team composition solve both regions
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.