head to head
Neither is simply harder - they are hard in different places. Portal 2 demands more execution; The Dig demands more variance.

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.

Optimization · Pure Optimization
A LucasArts sci-fi adventure where astronauts stranded on an alien world puzzle out its dead civilization.
Portal 2 leans Optimization (Pure Optimization); The Dig leans Optimization (Pure Optimization).
Portal 2 leans clearly harder on execution.
Portal 2
Portal placement requires some precision but timing is lenient.
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.
Portal 2
No opponent; puzzles are static.
The Dig
Alien world is static; companions follow scripts.
The Dig leans clearly harder on variance.
Portal 2
Puzzles are deterministic with no randomness.
The Dig
Alien machinery's purpose is hidden until experimented with.
Portal 2 leans clearly harder on optimization.
Portal 2
Solving the puzzle's logic IS the entire game.
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.