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

Optimization · Pure Optimization
A haunting puzzle-strategy game testing combo planning against rule-driven mortals.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Ghost Master leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Ghost Master
Assigning ghosts to fetters needs no dexterity
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.
Ghost Master
Mortal AI panics by rules, not by modelling you
Portal
No adversary modeling player.
Ghost Master leans clearly harder on variance.
Ghost Master
Mortal behaviour wanders but follows mappable logic
Portal
Deterministic chambers; no randomness.
Portal leans a little harder on optimization, though the gap is small.
Ghost Master
Ghost-power combos and plasm economy solve each haunting
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.