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

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.

Optimization · Pure Optimization
Open-world detective work testing evidence deduction without hand-holding.
Portal leans Optimization (Pure Optimization); The Sinking City leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
The Sinking City
Clunky combat is deliberately undemanding
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Portal
No adversary modeling player.
The Sinking City
Monsters and citizens follow fixed scripts
The Sinking City leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
The Sinking City
Case clues are hidden information until investigated
Portal leans clearly harder on optimization.
Portal
Pure puzzle-solving optimization.
The Sinking City
Cross-referencing evidence and city archives is the deduction core
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.