head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Optimization · Pure Optimization
Optimizing city placement, social policies, and victory routing under randomized map unknowns.

Optimization · Pure Optimization
A 3rd Edition ruleset combat puzzle where multi-classing and feat selection unlock dominant strategies.
Civilization V leans Optimization (Pure Optimization); Icewind Dale II 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.
Civilization V
UI actions need no precision; speed is not a factor
Icewind Dale II
Real-time-with-pause negates twitch requirements
Civilization V leans a little harder on reads, though the gap is small.
Civilization V
AI follows scripted personalities, not genuine player modelling
Icewind Dale II
Scripted enemy routines offer nothing to read or predict adaptively
Civilization V leans a little harder on variance, though the gap is small.
Civilization V
Random starts, barbarian spawns, and goody huts create hidden unknowns
Icewind Dale II
3E feat combinations and hidden enemy resistances create unknown-information layers
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Civilization V
Hex placement, social policies, and victory routing are fully solvable
Icewind Dale II
3rd Edition feat optimization and multi-class architecture dominate success
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.