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

Optimization · Pure Optimization
A chilly detective adventure investigating a deserted 1970s Quebec village locked in supernatural ice.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Kona leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Kona
Walking, driving, and light survival upkeep
Portal
Portal placement timing modest.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Kona
No opposition to outwit
Portal
No adversary modeling player.
Kona leans clearly harder on variance.
Kona
Mystery clues unknown until uncovered
Portal
Deterministic chambers; no randomness.
Portal leans clearly harder on optimization.
Kona
Investigation order and survival management are solvable
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.