head to head
Neither is simply harder - they are hard in different places. Endzone - A World Apart demands more variance; Portal demands more execution.

Optimization · Pure Optimization
Post-apocalyptic city builder about balancing water, radiation, and morale against random disasters.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Endzone - A World Apart leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Endzone - A World Apart
Pause-friendly mouse-driven management
Portal
Portal placement timing modest.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Endzone - A World Apart
No adaptive opposition
Portal
No adversary modeling player.
Endzone - A World Apart leans clearly harder on variance.
Endzone - A World Apart
Droughts, radiation, and raider events arrive semi-randomly
Portal
Deterministic chambers; no randomness.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Endzone - A World Apart
Resource chains and settlement layout are the whole game
Portal
Pure puzzle-solving optimization.
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.