head to head
Neither is simply harder - they are hard in different places. Metin2 demands more variance; Portal demands more execution.

Optimization · Pure Optimization
An oriental-fantasy grind MMORPG where upgrade luck and farming efficiency define progress.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Metin2 leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Metin2
Hack-and-slash grinding with simple inputs.
Portal
Portal placement timing modest.
Metin2 leans clearly harder on reads.
Metin2
Kingdom wars add light player-versus-player conflict.
Portal
No adversary modeling player.
Metin2 leans clearly harder on variance.
Metin2
Upgrade chance rolls dominate gear progression.
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.
Metin2
Farming spots, alchemy, and stat builds are solvable grind.
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.