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
Classic Roman city builder dominated by mastering its walker-based logistics.

Optimization · Pure Optimization
Sandbox city-builder where everything bends to optimization.
Caesar III leans Optimization (Pure Optimization); Cities: Skylines 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.
Caesar III
Mouse-driven building, no pressure
Cities: Skylines II
no mechanical demand
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Caesar III
Invasions are scheduled, not adaptive
Cities: Skylines II
no adversary
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Caesar III
Minor walker pathing unpredictability
Cities: Skylines II
minor sim noise
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Caesar III
Housing blocks and walker logistics are solvable systems
Cities: Skylines II
traffic, zoning, budgets 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.