head to head
Neither is simply harder - they are hard in different places. Master of Orion (2016) demands more variance; Portal demands more execution.

Optimization · Pure Optimization
Optimizing custom race design and tech priorities across a randomly generated galaxy.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Master of Orion (2016) leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Master of Orion (2016)
Turn-based menus; no physical demands at all
Portal
Portal placement timing modest.
Master of Orion (2016) leans clearly harder on reads.
Master of Orion (2016)
AI races follow defined personalities without adapting to your play
Portal
No adversary modeling player.
Master of Orion (2016) leans clearly harder on variance.
Master of Orion (2016)
Random galaxy generation and diplomatic outcomes add hidden elements
Portal
Deterministic chambers; no randomness.
Master of Orion (2016) leans a little harder on optimization, though the gap is small.
Master of Orion (2016)
Race design, tech priorities, and fleet composition are the solvable core
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.