head to head
Neither is simply harder - they are hard in different places. Divinity: Original Sin - Enhanced Edition demands more variance; Portal demands more execution.

Optimization · Pure Optimization
A turn-based RPG where system mastery and build optimization decide every fight.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Divinity: Original Sin - Enhanced Edition leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Divinity: Original Sin - Enhanced Edition
no real-time physical skill, turn-based
Portal
Portal placement timing modest.
Divinity: Original Sin - Enhanced Edition leans a little harder on reads, though the gap is small.
Divinity: Original Sin - Enhanced Edition
co-op has light unpredictability, mostly solo
Portal
No adversary modeling player.
Divinity: Original Sin - Enhanced Edition leans clearly harder on variance.
Divinity: Original Sin - Enhanced Edition
dice rolls and loot are randomized
Portal
Deterministic chambers; no randomness.
Divinity: Original Sin - Enhanced Edition leans a little harder on optimization, though the gap is small.
Divinity: Original Sin - Enhanced Edition
builds, combos, and tactics near-solvable
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.