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

Optimization · Pure Optimization
A survival city builder driven by harsh resource and law optimization.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Frostpunk leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Frostpunk
Pausable strategy with no input precision.
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.
Frostpunk
No adaptive opponent in the survival city.
Portal
No adversary modeling player.
Frostpunk leans clearly harder on variance.
Frostpunk
Scenario events and weather pulses add tension.
Portal
Deterministic chambers; no randomness.
Frostpunk leans a little harder on optimization, though the gap is small.
Frostpunk
Resource routing, laws, and heat 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.