head to head
Neither is simply harder - they are hard in different places. Imperium Galactica II: Alliances demands more reads; Portal demands more execution.

Optimization · Pure Optimization
A 4X space strategy game about building economy, tech and conquering fleets.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Imperium Galactica II: Alliances leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Imperium Galactica II: Alliances
Issuing orders has no twitch requirement
Portal
Portal placement timing modest.
Imperium Galactica II: Alliances leans clearly harder on reads.
Imperium Galactica II: Alliances
AI empires follow scripted strategies, not adaptive modelling
Portal
No adversary modeling player.
Imperium Galactica II: Alliances leans clearly harder on variance.
Imperium Galactica II: Alliances
Some randomness in combat and tech but bounded
Portal
Deterministic chambers; no randomness.
Imperium Galactica II: Alliances leans a little harder on optimization, though the gap is small.
Imperium Galactica II: Alliances
Empire economy, tech and fleet building is the whole game
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.