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

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

Optimization · Pure Optimization
A 1994 Sid Meier strategy game about building colonial economies and winning independence.
Fallout: New Vegas leans Optimization (Pure Optimization); Sid Meier's Colonization leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Sid Meier's Colonization
Turn-based; hands irrelevant
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Fallout: New Vegas
Scripted factions and enemies
Sid Meier's Colonization
Royal and rival AI behave on fixed schedules
Sid Meier's Colonization leans clearly harder on variance.
Fallout: New Vegas
Some loot and crit RNG
Sid Meier's Colonization
Random New World maps and native placement vary starts
Sid Meier's Colonization leans a little harder on optimization, though the gap is small.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
Sid Meier's Colonization
Production chains and liberty-bell timing are a solvable economy
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.