head to head
Neither is simply harder - they are hard in different places. Anno 1602 demands more variance; Portal demands more execution.

Optimization · Pure Optimization
Island colonisation strategy about balancing population tiers against expanding supply chains.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Anno 1602 leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Anno 1602
Slow real-time pace; no dexterity test.
Portal
Portal placement timing modest.
Anno 1602 leans a little harder on reads, though the gap is small.
Anno 1602
AI rivals act on fixed personalities, not adaptation.
Portal
No adversary modeling player.
Anno 1602 leans clearly harder on variance.
Anno 1602
Island fertility layouts and rival starts are hidden initially.
Portal
Deterministic chambers; no randomness.
Anno 1602 leans a little harder on optimization, though the gap is small.
Anno 1602
Population tiers and supply chains are a near-pure logistics solve.
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.