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

Optimization · Pure Optimization
Harsh village-builder; balance population, food, and winter.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Banished leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Banished
no mechanical layer
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.
Banished
no opponent
Portal
No adversary modeling player.
Banished leans clearly harder on variance.
Banished
weather, disease events
Portal
Deterministic chambers; no randomness.
Banished leans a little harder on optimization, though the gap is small.
Banished
population ratios and food planning
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.