head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is execution, and it is a single point.

Optimization · Systems & Chaos
A grim point-and-click testing puzzle persistence through a fixed descent into madness.

Optimization · Pure Optimization
A LucasArts sci-fi adventure where astronauts stranded on an alien world puzzle out its dead civilization.
Downfall leans Optimization (Systems & Chaos); The Dig leans Optimization (Pure Optimization).
Downfall leans a little harder on execution, though the gap is small.
Downfall
Clicking through scenes has no motor demand
The Dig
Point-and-click; no reflex demands.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Downfall
Characters are scripted psyches, not adapting opponents
The Dig
Alien world is static; companions follow scripts.
Downfall leans a little harder on variance, though the gap is small.
Downfall
Branching horrors are hidden until choices reveal them
The Dig
Alien machinery's purpose is hidden until experimented with.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Downfall
Puzzle chains and ending routes have fixed solutions
The Dig
Machine puzzles have single fixed solutions to deduce.
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.