head to head
Neither is simply harder - they are hard in different places. Portal demands more execution; Zeus: Master of Olympus demands more variance.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.

Optimization · Pure Optimization
A classic Greek city builder of housing blocks, gods, and mythic monsters.
Portal leans Optimization (Pure Optimization); Zeus: Master of Olympus leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
Zeus: Master of Olympus
Paused-friendly mouse planning
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Portal
No adversary modeling player.
Zeus: Master of Olympus
Rival cities act on schedules
Zeus: Master of Olympus leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
Zeus: Master of Olympus
Monster attacks and god visits semi-random
Zeus: Master of Olympus leans a little harder on optimization, though the gap is small.
Portal
Pure puzzle-solving optimization.
Zeus: Master of Olympus
Walker logic, housing blocks, and economy are deeply 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.