head to head
Neither is simply harder - they are hard in different places. Portal demands more execution; Tropico 6 demands more variance.

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

Optimization · Pure Optimization
Banana-republic management; juggle factions and the treasury.
Portal leans Optimization (Pure Optimization); Tropico 6 leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
Tropico 6
pausable management
Tropico 6 leans a little harder on reads, though the gap is small.
Portal
No adversary modeling player.
Tropico 6
factions scripted not adaptive
Tropico 6 leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
Tropico 6
election events, disasters
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Portal
Pure puzzle-solving optimization.
Tropico 6
economy and faction balance 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.