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

Optimization · Pure Optimization
A faction-driven RPG-shooter where build and route planning shape every ending.

Optimization · Pure Optimization
A 4X space strategy game about building economy, tech and conquering fleets.
Fallout: New Vegas leans Optimization (Pure Optimization); Imperium Galactica II: Alliances leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Imperium Galactica II: Alliances
Issuing orders has no twitch requirement
Imperium Galactica II: Alliances leans clearly harder on reads.
Fallout: New Vegas
Scripted factions and enemies
Imperium Galactica II: Alliances
AI empires follow scripted strategies, not adaptive modelling
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout: New Vegas
Some loot and crit RNG
Imperium Galactica II: Alliances
Some randomness in combat and tech but bounded
Imperium Galactica II: Alliances leans a little harder on optimization, though the gap is small.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
Imperium Galactica II: Alliances
Empire economy, tech and fleet building is the whole game
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.