head to head
Neither is simply harder - they are hard in different places. Portal demands more execution; Sid Meier's Civilization demands more variance.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.

Optimization · Pure Optimization
Long-horizon empire optimization over a randomly dealt but mappable map.
Portal leans Optimization (Pure Optimization); Sid Meier's Civilization leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
Sid Meier's Civilization
Turn-based clicking, zero physical demand
Sid Meier's Civilization leans a little harder on reads, though the gap is small.
Portal
No adversary modeling player.
Sid Meier's Civilization
AI leaders follow mappable personalities, not adaptive minds
Sid Meier's Civilization leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
Sid Meier's Civilization
Map generation and combat rolls hide early information
Sid Meier's Civilization leans a little harder on optimization, though the gap is small.
Portal
Pure puzzle-solving optimization.
Sid Meier's Civilization
Tech routing, expansion and economy are deeply solvable
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.