head to head
Neither is simply harder - they are hard in different places. Caesar IV demands more variance; Portal 2 demands more execution.

Optimization · Pure Optimization
Roman city builder about zoning, supply chains and keeping plebs and patricians content.

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.
Caesar IV leans Optimization (Pure Optimization); Portal 2 leans Optimization (Pure Optimization).
Portal 2 leans clearly harder on execution.
Caesar IV
Pause-friendly mouse management; no dexterity ceiling.
Portal 2
Portal placement requires some precision but timing is lenient.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Caesar IV
Invasions and gods are scripted, never adaptive.
Portal 2
No opponent; puzzles are static.
Caesar IV leans clearly harder on variance.
Caesar IV
Fires, plagues and barbarian timing add mild unknowns.
Portal 2
Puzzles are deterministic with no randomness.
Portal 2 leans a little harder on optimization, though the gap is small.
Caesar IV
Housing blocks, walker logistics and supply chains are solvable.
Portal 2
Solving the puzzle's logic IS the entire game.
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.