head to head
Neither is simply harder - they are hard in different places. Portal 2 demands more optimization; Sherlock Holmes: The Devil's Daughter demands more variance.

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

Optimization · Pure Optimization
Investigation and deduction-tree logic with token action interludes.
Portal 2 leans Optimization (Pure Optimization); Sherlock Holmes: The Devil's Daughter leans Optimization (Pure Optimization).
Portal 2 leans a little harder on execution, though the gap is small.
Portal 2
Portal placement requires some precision but timing is lenient.
Sherlock Holmes: The Devil's Daughter
Occasional action minigames, mostly trivial
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.
Sherlock Holmes: The Devil's Daughter
Suspects are written characters, not adapting minds
Sherlock Holmes: The Devil's Daughter leans clearly harder on variance.
Portal 2
Puzzles are deterministic with no randomness.
Sherlock Holmes: The Devil's Daughter
Case clues are hidden until investigated
Portal 2 leans clearly harder on optimization.
Portal 2
Solving the puzzle's logic IS the entire game.
Sherlock Holmes: The Devil's Daughter
Deduction-tree reasoning from gathered evidence is the game
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.