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

Optimization · Pure Optimization
A sandbox city builder that is pure traffic and zoning optimization.

Optimization · Pure Optimization
A perfect-information tactics puzzle solved one turn at a time.
Cities: Skylines leans Optimization (Pure Optimization); Into the Breach 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.
Cities: Skylines
No reflex demands at all.
Into the Breach
No mechanical inputs
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Cities: Skylines
No adaptive opponent exists in the sandbox.
Into the Breach
Enemy moves telegraphed fully each turn
Into the Breach leans a little harder on variance, though the gap is small.
Cities: Skylines
Minor disaster events if enabled.
Into the Breach
Light spawn and squad randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Cities: Skylines
Traffic flow, zoning, and budgets are fully solvable.
Into the Breach
Pure puzzle - perfect-information chess each turn
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.