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

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

Optimization · Pure Optimization
The 1996 landmark 4X where you guide a civilization from antiquity to the space race.
Fallout: New Vegas leans Optimization (Pure Optimization); Sid Meier's Civilization II leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Sid Meier's Civilization II
Turn-based clicking only
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Fallout: New Vegas
Scripted factions and enemies
Sid Meier's Civilization II
AI civs are exploitable scripts, not adaptive rivals
Sid Meier's Civilization II leans clearly harder on variance.
Fallout: New Vegas
Some loot and crit RNG
Sid Meier's Civilization II
Random maps and hut rolls inject early uncertainty
Sid Meier's Civilization II leans a little harder on optimization, though the gap is small.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
Sid Meier's Civilization II
City spacing, trade routes and tech paths 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.