head to head
Neither is simply harder - they are hard in different places. Duck Detective: The Ghost of Glamping demands more variance; Portal demands more execution.

Optimization · Pure Optimization
A deduction mystery testing fitting gathered clues into logical conclusions.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Duck Detective: The Ghost of Glamping leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Duck Detective: The Ghost of Glamping
Clicking clues demands no dexterity
Portal
Portal placement timing modest.
Duck Detective: The Ghost of Glamping leans a little harder on reads, though the gap is small.
Duck Detective: The Ghost of Glamping
Suspects follow scripted dialogue, no adaptation
Portal
No adversary modeling player.
Duck Detective: The Ghost of Glamping leans clearly harder on variance.
Duck Detective: The Ghost of Glamping
Clues hidden until inspected each case
Portal
Deterministic chambers; no randomness.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Duck Detective: The Ghost of Glamping
Fitting evidence into deduction blanks is the whole puzzle
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.