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

Optimization · Pure Optimization
A 90s-set mystery adventure following a motorcycle-riding journalist into her hometown's secrets.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Kathy Rain leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Kathy Rain
No physical demands
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.
Kathy Rain
No adaptive opponent
Portal
No adversary modeling player.
Kathy Rain leans clearly harder on variance.
Kathy Rain
Mystery beats are hidden only until discovered
Portal
Deterministic chambers; no randomness.
Portal leans a little harder on optimization, though the gap is small.
Kathy Rain
Fixed puzzle and dialogue chain; one solution path
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.