head to head
Neither is simply harder - they are hard in different places. Operencia: The Stolen Sun demands more variance; Portal demands more execution.

Optimization · Pure Optimization
A turn-based dungeon crawler testing party building and methodical dungeon mapping.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Operencia: The Stolen Sun leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Operencia: The Stolen Sun
Turn-based combat removes any physical ceiling
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.
Operencia: The Stolen Sun
Encounters are scripted, no adaptive mind
Portal
No adversary modeling player.
Operencia: The Stolen Sun leans clearly harder on variance.
Operencia: The Stolen Sun
Dungeon secrets and loot are hidden until mapped
Portal
Deterministic chambers; no randomness.
Portal leans a little harder on optimization, though the gap is small.
Operencia: The Stolen Sun
Party builds and turn sequencing 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.