head to head
Neither is simply harder - they are hard in different places. Kona demands more variance; Portal 2 demands more optimization.

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

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.
Kona leans Optimization (Pure Optimization); Portal 2 leans Optimization (Pure Optimization).
Portal 2 leans clearly harder on execution.
Kona
Walking, driving, and light survival upkeep
Portal 2
Portal placement requires some precision but timing is lenient.
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 2
No opponent; puzzles are static.
Kona leans clearly harder on variance.
Kona
Mystery clues unknown until uncovered
Portal 2
Puzzles are deterministic with no randomness.
Portal 2 leans clearly harder on optimization.
Kona
Investigation order and survival management are solvable
Portal 2
Solving the puzzle's logic IS the entire game.
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.