head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Optimization · Pure Optimization
The 2001 Civilization entry that introduced culture, strategic resources and refined empire micromanagement.

Optimization · Pure Optimization
A 1994 Sid Meier strategy game about building colonial economies and winning independence.
Sid Meier's Civilization III leans Optimization (Pure Optimization); Sid Meier's Colonization leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Sid Meier's Civilization III
No dexterity in a turn-based interface
Sid Meier's Colonization
Turn-based; hands irrelevant
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Sid Meier's Civilization III
AI personalities are fixed and mappable
Sid Meier's Colonization
Royal and rival AI behave on fixed schedules
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Sid Meier's Civilization III
Random maps, resources and combat rolls matter early
Sid Meier's Colonization
Random New World maps and native placement vary starts
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Sid Meier's Civilization III
Corruption math, worker turns and culture borders reward deep optimization
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.