head to head
Neither is simply harder - they are hard in different places. Portal demands more optimization; Squad Assault: Second Wave demands more variance.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Optimization · Pure Optimization
A tactical squad-based shooter set in modern warfare scenarios.
Portal leans Optimization (Pure Optimization); Squad Assault: Second Wave leans Optimization (Pure Optimization).
Portal leans a little harder on execution, though the gap is small.
Portal
Portal placement timing modest.
Squad Assault: Second Wave
tactical shooting inputs, moderate demand
Squad Assault: Second Wave leans a little harder on reads, though the gap is small.
Portal
No adversary modeling player.
Squad Assault: Second Wave
scripted enemy AI squads, not adaptive
Squad Assault: Second Wave leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
Squad Assault: Second Wave
random mission events and encounters
Portal leans clearly harder on optimization.
Portal
Pure puzzle-solving optimization.
Squad Assault: Second Wave
squad tactics and loadout 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.