head to head
Neither is simply harder - they are hard in different places. Emperor: Rise of the Middle Kingdom demands more variance; Portal 2 demands more execution.

Optimization · Pure Optimization
Ancient China city builder about elegant housing-block logistics.

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.
Emperor: Rise of the Middle Kingdom leans Optimization (Pure Optimization); Portal 2 leans Optimization (Pure Optimization).
Portal 2 leans clearly harder on execution.
Emperor: Rise of the Middle Kingdom
Pausable city placement, no pressure
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.
Emperor: Rise of the Middle Kingdom
No adaptive opposition
Portal 2
No opponent; puzzles are static.
Emperor: Rise of the Middle Kingdom leans clearly harder on variance.
Emperor: Rise of the Middle Kingdom
Invasions and events on known schedules
Portal 2
Puzzles are deterministic with no randomness.
Portal 2 leans a little harder on optimization, though the gap is small.
Emperor: Rise of the Middle Kingdom
Walker logistics and feng shui block planning
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.